Scepticism and hypothetical method

ELENCHOS

Collana di testi e studi sul pensiero antico

fondata da

GABRIELE GIANNANTONI

LIX

ELENCHOS

Collana di testi e studi sul pensiero antico

Direttore:ENRICO BERTI

Comitato scientifico:FRANCESCA ALESSE, ENRICO BERTI, ALDO BRANCACCI,

GIUSEPPE CAMBIANO, ANNA MARIA IOPPOLO,CLAUDIO MORESCHINI, RICCARDO POZZO, MARIO VEGETTI

Cura redazionale:MARIA CRISTINA DALFINO

ISTITUTO PER IL LESSICO INTELLETTUALE EUROPEO E STORIA DELLE IDEE

ARGUMENT FROM HYPOTHESIS IN ANCIENT PHILOSOPHY

Edited by ANGELA LONGO

with the collaboration of DAVIDE DEL FORNO

BIBLIOPOLIS

ISBN 978-88-7088-597-2

Copyright © 2011 byC.N.R., Istituto per il Lessico Intellettuale Europeo e Storia delle Idee

Volume pubblicato con il contributo del Fondo nazionale svizzero

per la ricerca scientifica

Il volume è stato sottopostoall’approvazione di

Enrico Berti e Giuseppe Cambiano

Proprietà letteraria riservata

ACKNOWLEDGEMENTS

The present volume is closely linked to the scientific pro-ject “The concept and the use of dialectic in the Platonicschools of Athens and Alexandria between the fifth and thesixth centuries AD”. The project, which I had the privilege tosupervise, was funded by the Swiss National Science Founda-tion. I would like to offer my sincere thanks to this institutionfor its support.

I am very grateful to Davide del Forno for the help he pro-vided in the first phase of the editorial job and in the compila-tion of the indexes.

My warmest thanks go to Jonathan Barnes not only for histranslation of the volume’s introduction from Italian into Eng-lish, but also for his generosity in making the offer.

Finally, I should like to thank Enrico Berti for offering thebook a place in the Collana “Elenchos”, and Maria CristinaDalfino for her invaluable technical aid in the preparation ofthe text.

CONTENTS

Introduction p. 11

PART I: PLATO AND ARISTOTLEV. KARASMANIS: ’Apagwghv: Hippocrates of Chiosand Plato’s Hypothetical Method in the Meno » 21F. FRONTEROTTA: ‘Upovqesi" e dialevgesqai. Meto-do ipotetico e metodo dialettico in Platone » 43C. CHIESA: La réfutation socratique et la métho-de hypothétique » 75P. CRIVELLI: Aristotle on Syllogisms from aHypothesis » 95

PART II: HELLENISTIC PHILOSOPHYJ. BARNES: Reading the Hypotheticals » 187L. CORTI: Scepticism and Hypothetical Method » 281J.-B. GOURINAT: Hypothèse et hypothétique chezAlcinoos et Galien » 303

PART III: LATE PLATONISMD. DEL FORNO: Le rapport entre la méthodehypothétique et les quatre autres procédés de ladialectique dans le Ve livre du Commentaire deProclus sur le Parménide de Platon » 345D. D. BUTORAC: The Place and Purpose of Hy-potheses in Proclus: Method, Training and Sal-vation » 365

A. LERNOULD: De la logique à la théologie. Lespreuves démonstratives dans le Timée de Platonselon Proclus p. 383F. TRABATTONI: Le “silence de Platon”, ou le ren-versement du discours dialectique chez Damascius » 413

Texts » 437Bibliography » 441Index of passages » 451Index of ancient and medieval authors » 467Index of modern authors » 471

10 CONTENTS

LORENZO CORTI

(Fonds National Suisse / University of Cambridge)

SCEPTICISM AND HYPOTHETICAL METHOD*

1. Exordium

Anyone who undertakes to write a paper on scepticismand hypothetical method in Antiquity must face two empiricaldifficulties. If he is to deal with the sceptic criticism of the Pla-tonic hypothetical method (the heuristic device sketched byPlato in the Meno), he must face the non-existence of such asubject: our main source for ancient scepticism, Sextus Empir-icus, does not attack Platonic hypothesizing, but rather whatwe may call Aristotelian hypothesizing – the reasonableness ofposing the axioms or principles of sciences. If one were todecide to start from Sextus’ attack on axioms, he would meet asecond and even more threatening obstacle: Sextus’ criticismhas been already analyzed by Jonathan Barnes in his Toils ofScepticism1.

* This paper is an outcome of my research project “Scepticism andMetaphysics in Greek Antiquity”, financed by the Swiss National Foun-dation (PA0011-115325). I would like to thank this institution for its sup-port. The paper has particularly benefitted from remarks from JonathanBarnes, Paolo Crivelli, Vassilis Karasmanis, Angela Longo, David Sedleyand Myrto Hatzimichali, who has also purified my English. I am verygrateful to them all.

1 See J. BARNES, The Toils of Scepticism, Cambridge University Press,Cambridge 1990, pp. 90-112.

Pygmaei gigantum humeris impositi plus quam ipsi gigantesvident. In this paper I will inquire into the relationshipsbetween Sextus’ scepticism and the two kinds of hypotheseswhich I have just hinted at. I will firstly put forward a sketch ofthe dialectic between sceptics and dogmatists concerning theAristotelian hypotheses – starting (and drawing) from Barnes’analysis, and then dealing with some texts and some issues heonly partially covered. I will then try to see if and how, giventhe differences between Aristotelian hypotheses and Platonichypotheses, the sceptic objections and the dogmatic repliesabout the former can be applied to the latter.

2. Sextus’ Attack on Axioms

Sextus attacks the Aristotelian hypotheses using the socalled “hypothetical” mode of suspension of judgement. Thehypothetical mode belongs to a group of schemas of argu-ments, Agrippa’s modes, by which the sceptic achieves his sus-pension of judgement about any issue whatsoever. A detailedaccount of Agrippa’s modes is well beyond the scope of thisarticle; but in order to understand Sextus’ attack, we have toprovide a sketch of Sextus’ radical sceptic and of his use of themodes.

The sceptic is an inquirer capable of suspending his judge-ment about any issue of inquiry: someone who, given anyproposition P, after having considered the possibility that P,does not judge either that P or that not-P (does not assenteither to P or to not-P). The sceptic reaches his suspension byusing different groups of argument patterns called the “modesof suspension of judgement”. The hypothetical mode belongsto one of the most powerful groups of such patterns: Agrippa’smodes. These modes work, roughly, as follows. Suppose thatyou think to assent to a proposition P. Either you have some-thing to say in favour of P, or nothing at all. If you have noth-ing to say in favour of P, then you must not assent to it (that is

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the hypothetical mode). If you have something to say in favourof P, say Q, then either Q is the same as P, or it is not. If Q isthe same as P, then you should suspend your judgement aboutP – for, in this case you are using a circular, invalid argument(reciprocal mode). If Q is not the same as P, then either youhave nothing to say in favour of Q (and if so, you must sus-pend your judgement on Q and therefore on P), or you havesomething to say in its favour – say R. Then we can say about Rwhat we have just said about Q; and you will avoid suspensionof judgement only by introducing a new proposition, S; and soon ad infinitum. But you cannot go on ad infinitum; so youmust suspend your judgement about P2.

Let us take a closer look at the hypothetical mode – at Sex-tus’ arguments against hypotheses. These are to be found in hisOutlines of Scepticism (PH I 173-174), Against the Logicians (MVIII 369-378) and Against the Geometers (M III 7-17). We willstart from M III. At the beginning of his inquiry on geometrySextus distinguishes three ways in which things are calledhypotheses. In M III 14, he points out that

in a third sense, we call hypotheses the first principles of proofs;for a hypothesis is the postulating of a fact for the establishing ofsomething.

This, he adds a little later, is the sort of hypothesis whichhe is going to investigate. When Sextus talks about thehypotheses of the geometers, then, he has in mind a way ofproving something which begins by laying down, or hypothe-sizing, certain propositions as first principles:

The geometers, seeing the mass of problems which dog them,retreat into what they think to be a matter safe and free from dan-ger, namely the postulating of the first principles of geometry (th'"gewmetriva" ajrcaiv) by hypothesis (M III 1).

SCEPTICISM AND HYPOTHETICAL METHOD 283

2 This is an outline of Barnes’ interpretation of Agrippa’s modes: seeJ. BARNES, The Toils of Scepticism, cit., pp. 113-120.

Sextus’ use of the word uJpoqevsei" to denote the ajrcaiv ofsuch a science as geometry has an Aristotelian origin. In hisAn. post. 72a20-24, Aristotle holds that among the first princi-ples or ajrcaiv on which any science is based there are hypothe-ses. Hypotheses are, in this sense, a species of what we callaxioms, the first principles from which the remaining truths ortheorems of a science are derived. After Aristotle, though,especially in the post-Hellenistic era, the term uJpovqesi" cameto be used also in a broader way, in order to denote all firstprinciples, not merely a species of them. Alexander of Aphro-disias, for instance, points out that

hypotheses are first principles of proofs, because there is no proofof such propositions, i.e. of first principles, but they are posited asevident and known in themselves […] and what is assumed with-out proof they call a hypothesis […] and say that is hypothesized(in An. pr. 13, 7-11)3.

Sextus, in M III, targets the axioms or first principles ofgeometry. He wants to show that the act of a geometer such asEuclid of laying down certain propositions as the axioms of hisgeometrical system – say «Things which are equal to the samething are also equal to one another» – is unreasonable; and hewants to do that by showing that the act of posing any axiomin general is unreasonable. In order to see Sextus’ point, it isuseful to stress two crucial features of such an act. Layingdown, or hypothesizing, a proposition P as an axiom of a sci-ence is a part of a “demonstrative” activity: the axiom is astarting point in the demonstration of truths – the theorems ofthat science. Now, in laying down P as an axiom one, ofcourse, commits himself to the truth of P: Euclid, in hypothe-sizing the above mentioned proposition at the beginning of his

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3 Other examples of this use are to be found in Sextus (PH I 183, MIX 2, 419; M VI 5), Galen (Sect. int. I 93 K., Us. part. III 45-46 K.; Loc. aff.VIII 324, 316 K.; Lib. prop. XIX 43 K.) and Proclus (in Eucl. 76, 24-77, 3;cf. 178, 1-14).

Elements, accepts that that proposition is true. On the otherhand, in laying down P as an axiom one does not argue that P.He does not argue that P because, if P really is an axiom, hecannot argue that P. Axioms or first principles are things forwhich no argument is possible: they cannot, by definition, beknown on the basis of anything else.

Sextus is well aware of this feature of hypothesizing. At thebeginning of his discussion of hypotheses in M III 7, heremarks that

those who assume something by hypothesis and without proofare satisfied by a bare assertion alone.

Making a bare assertion (yilh; favsi"), in Sextus writings,contrasts with offering an argument or reason for an assertion4:to make a bare assertion is merely to assert. Thus, Sextusobserves rightly that the dogmatists, in hypothesizing that P,assert, and do nothing more than assert that P – indeed, theycannot offer any argument in favour of their hypotheses.

But what is wrong with the dogmatist’s barely asserting?Sextus’ strongest case appears in M VII 315:

The dogmatist will not simply assert. For then one of his oppo-nents will utter the assertion which claims the opposite, and inthis way the former will be no more warranted than the latter –for one bare assertion is worth the same as another.

Sextus’ point is simple and effective. Given any proposi-tion P hypothesized by a dogmatist, there will always be aproposition incompatible with P, say not-P, which we mayhypothesize; and just as hypothesizing that P warrants the dog-matist in believing that P, hypothesizing that not-P warrants usin believing that not-P. In other words, if it is legitimate tohypothesize that P, then it is equally legitimate to hypothesize


4 See J. BARNES, The Toils of Scepticism, cit., p. 97 for details.

that not-P. For, if each of P and not-P are bare assertions, wehave no reason to prefer P to not-P – or vice versa.

Thus, the core of Sextus’ argument, according to Barnes’analysis, runs as follows. If you advance P as a hypothesis – ifyou lay down P as a first principle, then by definition you nei-ther argue for P nor allege anything at all in its favour – yourutterance of P is a bare assertion. But then someone elsehypothesizes a proposition incompatible with P – say not-P.There is nothing to be said for P which cannot be said for not-P, or vice versa, since there is nothing at all to be said for P andnothing at all to be said for not-P. If there were, they would notbe being hypothesized. And if this is so, why should one acceptP rather than not-P?

Two points need clarification. First: Sextus might be takento suggest that there is no alternative between making a bareassertion and making an assertion supported by an argument.This is not so: you can defend an assertion you have madeoffering something which is not, strictly speaking, an argumentfor it. Aristotle, in Metaph. G 3, asserts the Law of Contradic-tion. He then puts forward remarks which are not to be takenas a proof of it (for, as he stresses, such a proof does not exist),but still constitute a defence of it. From the point of view ofAgrippa’s modes, though, this distinction is not relevant. If youclaim something to defend your assertion that P, say Q, be Qan argument in favour of P or something else, then you aregrounding your belief that P on your belief that Q; and this isenough for Agrippa’s modes to be applicable to Q, and to pro-duce your suspension of judgement on Q (and on P). Second:Sextus, in M III, targets the first principles of geometry, whichare not the first principles of science – things like the Law ofContradiction. But science is founded on its first principlesjust like geometry is founded on its first principles; and, as wehave seen, Sextus aims to show the unreasonableness of thefirst principles of geometry by showing the unreasonablenessof any first principle whatsoever. Thus, by attacking the hypo-thetical method of the geometers, Sextus is attacking the foun-dation of all dogmatic knowledge.

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3. A Dogmatic Reply: Natural Epistemology

Many dogmatists react to this kind of objection by urgingthat there are some propositions such that, despite the fact thatwe do not have any argument in their favour, we reasonablyaccept them – we are justified in believing them. This claim hasbeen made, famously, by Aristotle in An. post. A 3. In this pas-sage Aristotle is concerned with the general possibility of sci-entific knowledge or ejpisthvmh, and hence he is implicitly con-cerned with scepticism. He considers the possibility that theknowledge of any proposition must be based on the knowl-edge of some other proposition: that if you know that P, thenyou must base this knowledge on your knowledge of – say – Q.But this characterization is threatened by an infinite regress: ifyou know that P, then you must know that Q; but if you knowthat Q, then you must know that R, and so on; so that if youknow something, you know an infinite number of things – andthis is impossible. On the basis of this argument, Aristotlereminds us, some thinkers have concluded that knowledge isimpossible. Aristotle reacts to the threat by arguing that insome cases we may properly claim to know something even ifour knowledge is not based on the knowledge of anotherclaim: that at some point of our epistemological sequence wemay, with reason and justification, barely assert (hypothesize) anew proposition.

Almost all dogmatists, following Aristotle, try to charac-terise a class of propositions which may be properly hypothe-sized – which we may reasonably accept as hypotheses. Thesepropositions form the basis of our system of justified beliefs:they constitute the foundation of our knowledge. The dogma-tists, then, putting forward the so called “foundationalist”epistemologies, divide our items of knowledge or our justifiedbeliefs into two classes: the fundamental or basic, and thedependent or derivative. I know something in a derivative wayif this knowledge is based on another piece of knowledge (jus-tified belief) of mine; I know something in a direct way if this


piece of knowledge is not based on another piece of knowl-edge of mine. This distinction is represented in Sextus by thedistinction between propositions which are known by a criteri-on of truth (basic beliefs) and propositions which are knownby signs or proofs (derivative beliefs).

In many cases, the dogmatists characterise the basic beliefsby putting forward an externalist account of them. Someone’sbeliefs may be justified by reference to some further beliefs ofhis, or by reference to something, a fact, which is not a belief ofhis. For instance, I believe both that there are invisible pores inmy skin, and that I sweat. But the causal story of my two beliefsis different. I came to believe that there are invisible pores inmy skin by making an inference from another belief of mine:the belief that I sweat. I came to believe that I sweat just feelingthat I sweat. My basic belief that I sweat, like all basic beliefson this account, has an external justification; it is justified notby an epistemic state of mine, but by something external to mybelief system: the fact that I sweat.

Now, a dogmatist who embraces a foundationalist episte-mology and an externalist account of basic beliefs seems to beable to give an effective reply to Sextus’ objection against hishypothesizing that P. The dogmatist reasonably accepts/is jus-tified in believing that P (rather than not-P), without havingany reason for believing that P, because P belongs to the classof basic beliefs (and not-P does not); and a basic belief is suchthat the dogmatist’s believing that P is grounded not on anybelief on his part, but on a fact external to his belief system.Thus basic beliefs are grounded, but are grounded on some-thing which is not an epistemic state of the dogmatist.

Some philosophical texts of Antiquity present differentspecies of a theory, that of “natural epistemology”, which canbe understood as an externalist account of basic beliefs. Wefind this theory fully expressed in Galen, but traces of it can befound even earlier – especially in Stoic and Stoic influencedtexts. Let us start with a passage from Galen’s essay against theAcademic sceptic Favorinus:

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It is plainly evident to us that there is something securely known,even if the sophists have done their best to make it untrustworthy,saying that there is no natural criterion. A pair of compassesdescribes a circle; a rule determines lengths, just as a balancedetermines weights. Man has created these things on the basis ofnatural organs and criteria, beyond which we have no more vener-able and honourable criterion (Opt. doct. I 48-49 K.)5.

We construct artificial criteria of truth, artificial yardsticksfor determining the shapes and sizes and weights of things.And we do that on the basis of the natural criteria we possess.What are these natural criteria? Galen’s answer appears in hisDoctrines of Hippocrates and Plato:

Nature has given us two things: the criteria themselves, anduntaught trust in them. Now the criteria themselves are the sense-organs and the faculties which use these organs; and an untaughtand natural trust in them is found not only in men but in the otheranimals too (PHP V 725 K.).

Just as we determine whether a stick is one meter longusing our artificial criterion of truth (aptly applying the rulerto the stick), so we determine whether it is raining using ournatural criterion of truth (opening and orientating our eyes tothe sky). If our eyes report that it is raining, and our senses andour minds are in their natural state, then we will know that it israining.

According to the externalist account, basic beliefs aregrounded on some facts external to the believer – the believercomes to have them not by means of an inference from otherbeliefs of his, but by using a criterion of truth. For the Stoics,as for Galen, such a criterion includes sense perception andthe non-epistemic impressions caused by sense perception. AsSextus reports in M VII 259:


5 For the passages from Galen’s Opt. doct. I have used a slightly mod-ified version of R.J. HANKINSON’s translation in The Cambridge Compan-ion to Galen, Cambridge University Press, Cambridge 2008, p. 162.

Nature has given us our perceptual faculty and the impressionswhich arise through it as, so to speak, a light for the recognition oftruth, and it would be absurd to reject such a faculty and todeprive ourselves of, as it were, the light.

A little earlier, describing the views of the “more recent”Stoics, Sextus remarks that

the criterion of truth is the apprehensive impression – not withoutqualification, but when there is no obstacle. For this, they say, isevident and striking, and it all but grasps our hair and drags us toassent (M VII 257).

By nature we are provided with a faculty for determiningthe truth – that of perceiving and having apprehensive impres-sions; and by nature we are dragged to assent to the prompt-ings of the faculty. Our apprehensive impressions – the psy-chological experiences caused by sense perception in virtue ofwhich we acquire basic beliefs about the world – form a natur-al class of experience:

The Stoics say that […] an apprehensive impression […] has aspecial character distinguishing it from other impressions, just ashorned snakes differ from other snakes (M VII 252).

Horned snakes are a special class of snakes, distinguishedfrom the other snakes by a natural feature; similarly, apprehen-sive impressions are a special class of impressions, distin-guished by nature from other and unreliable impressions6.

There are two kinds of things which nature determines usto believe; first of all, simple perceptual propositions such as«It is raining». Secondly – at least, according to Galen – princi-ples. Thus, among the items which Galen defends from theacademic attack by introducing his natural epistemology, wefind the above mentioned first axiom of Euclid’s Elements:

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6 For this interpretation of Sextus’ account of the Stoic apprehensiveimpression see J. BARNES, The Toils of Scepticism, cit., pp. 134-135.

Things which are equal to the same thing are also equal to oneanother (Opt. doct. I 45, 50 K.).

Elsewhere, Galen generalises this claim by pointing outthat

it is by nature that all men possess certain first principles of reason(logikai; ajrcaiv) (Thrasyb. V 846-847 K.).

We believe the first principles or ajrcaiv because naturerequires us to believe them: our beliefs are naturally deter-mined.

Reference to nature, here, is reference to natural or causalconnection. Certain states of affairs are such that, once theycome to our attention (i.e. once they are the object of a non-epistemic impression of ours), we are thereby caused to believethat they obtain. On this view, “basic” beliefs are what may betermed “natural” beliefs; and natural beliefs are those beliefstowards which nature leads us, i.e. those beliefs which we arenaturally caused to have by the very facts which the beliefsexpress. We might say that x has a “natural/basic belief” that Pjust in case (i) it is the fact that P which causes it to seem to xthat P; and (ii) it is the fact that it seems to x that P which caus-es x to believe that P7.

According to a Stoic theory reported elsewhere (M VIII

397) by Sextus, we acquire some of our justified beliefs aboutthe world in a twofold process. First, we are stricken by animpression – a certain thought presents itself to our mind; andsecond, we assent to the thought: we judge true the thoughtwhich has come to our mind. The first step is involuntary; thesecond is voluntary: we use our faculty of judging, and wemake a choice. Natural beliefs are not like that. For, in the caseof natural belief, it is the fact itself that it seems to us that Pthat causes us to believe that P. We face here a distinction


7 Cf. ibid., p. 136.

between beliefs which are caused by an antecedent judgementabout their object, and beliefs which are not-caused by anantecedent judgement about their object. As far as the dog-matic theory goes, our beliefs about the principles of sciences(e.g. geometry) belong to the second class just as our beliefsabout perceptible states of affairs: we come to have the beliefthat it is raining not by having judged, after reflection, that thisis so, but by having had the non-epistemic impression that thisis so, caused by fact that it is raining; we come to believe theElements’ first axiom not by having judged, after reflection,that this proposition holds, but by having had the non-epis-temic impression that this is so, caused by the correspondingfact.

4. A Sceptic Reply to Natural Epistemology, and the Dogma-tic “So what?” Reply

Had the Pyrrhonists any reply to this dogmatic move?Barnes’ look is sharp enough to find one in Sextus’ account ofa celebrated fragment of the pre-Socratic philosopher Xeno-phanes of Colophon in M VII 49 and 528. In the following linesI will not discuss these passages, but just sketch the Pyrrhon-ian reply as it results from Barnes’ interpretation. Suppose theDogmatist hypothesizes that P – offers P as a putative item ofbasic knowledge. The Pyrrhonist asks whether the Dogmatistreasonably accepts/is justified in claiming that P, since he hasno reason in its favour. Now the Dogmatist, on the externalisthypothesis, will be justified in claiming that P provided that hebelieves that P because P belongs to the class of basic beliefs –provided that his belief that P is grounded not on any otherbelief of his, but on a fact external to his belief system. But thedogmatist cannot reply to the sceptic’s question claiming thathe believes that P because P belongs to the class of basic

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8 See ibid., pp. 138-144.

beliefs. For, the whole point of his externalist invocation ofbasic beliefs is that he may justifiably believe that P withoutmaking the further claim that he believes that P because Pbelongs to the class of basic beliefs. Indeed, if he made thatclaim, he would ground his belief that P on another belief ofhis, and thus his belief that P would not be basic anymore: itwould become derivative, and as such subject to Agrippa’smodes. So how will the Dogmatist react to the sceptic’s attack?If he keeps maintaining that P, then he is maintaining some-thing which he does not believe he is justified in maintaining.It is not that he confesses, under pressure from the Pyrrhonist,that he is not justified in believing that P; he suspends hisjudgement over this question. Now it is, of course, perfectlypossible to believe that P while not believing that you are justi-fied in believing that P – suspending your judgement on thematter. But is this a rational state of mind to be in? Can I ratio-nally say «I believe that it is raining, but I don’t think that I amjustified in believing that it is raining?»

Let me exemplify the scenario that this last sceptic moveleaves us with. The dogmatist believes that it is raining, andthis is a basic belief of his. Indeed, he has come to have thisbelief not by means of other beliefs of his, but in the follow-ing way: the fact that it is raining has caused in him the non-epistemic impression that this is so; and his non-epistemicimpression that it is raining has caused him to believe thatthis is so. On the other hand, because of the sceptic attack,the dogmatist does not believe that he believes that it is rain-ing because «It is raining» belongs to the class of basic beliefs– he suspends his judgement on that. «But if this is so» – thesceptic asks the dogmatist – «can you say that you are ratio-nally accepting that it is raining»? No; therefore, you shouldsuspend your judgement over the question whether it is rain-ing. And so Barnes ends his Toils of Scepticism on a scepticalnote9.


9 See ibid., p. 144.

But maybe there are other notes to play? At this stage ofthe sceptical attack against the Aristotelian hypothesis, I find ittempting to recall a dogmatic move which has been made first-ly by Galen and developed, a few centuries later, by DavidHume – what I will call the “So what?” reply. Let us start withGalen, and see how the passage of his Opt. doct. we had a lookat a while ago continues. Talking about the natural criteria oftruth, i.e. our senses in our natural condition, Galen observes:

So if we must begin from there – for mind tells us once again thatwhile we may trust or distrust our natural criterion, we cannotjudge it by means of something else: for how could this thing, bywhich everything else is judged, be judged by something else? –will you wish to place your trust in eyes which are seeing clearlyand a tongue which is tasting as to the fact that this is an appleand that a fig? If you don’t, I will suffer what you want to do to us;but if you do want to dispute <with me, then I am ready to do soprovided that you do place your trust in them>; but if you don’t,then I will simply leave, since you are not in a natural condition(Opt. doct. I 49 K.).

The reply sounds as follows. Here are the sceptical argu-ments against the criterion of truth/against hypothesizing.There is no answer to them – since we cannot in principle findan answer to them. So what to do? We have a choice. We candecide either, despite the sceptic’s arguments, to accept some-thing and reject something; or, because of the sceptic’s argu-ments, to accept nothing. But even if we have a choice, thischoice is not free. For, rejecting the criterion is against nature(para; fuvsin). In other words, as we have seen, we have such anature that, whatever we decide to do, we will accept some-thing (and reject something else). Nature pushes us towardssome acceptations. This idea has been developed by D. Humein a well known passage of his Treatise (p. 269) in which heavows his reaction to the sceptical arguments:

Where am I, or what? From what causes do I derive my existence,and to what condition shall I return? [...] I am confounded with

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all these questions, and begin to fancy myself in the mostdeplorable condition imaginable, inviron’d with the deepest dark-ness, and utterly depriv’d of the use of every member and faculty.Most fortunately it happens, that since reason is incapable of dis-pelling these clouds, nature herself suffices to that purpose, andcures me of this philosophical melancholy and delirium, either byrelaxing this bent of mind, or by some avocation, and livelyimpression of my senses, which obliterate all these chimeras. Idine, I play a game of back-gammon, I converse, and am merrywith my friends; and when, after three or four hours’ amusement,I wou’d return to these speculations, they appear so cold, andstrain’d, and ridiculous, that I cannot find in my heart to enterinto them any farther.

Let’s analyse the “So what?” reaction. It is impossible tofind a reply to the sceptical arguments against hypothesizing.For, in order to do so, we should be capable of showing thatour criterion of truth – the instrument using which we come tohave our basic beliefs – is correct. In other words, we shouldbe capable of judging our criterion of truth; but if “that” is ourcriterion of truth, using which criterion could we judge it?Thus, we cannot discuss our criterion of truth, but eitheraccept or reject it. Therefore we cannot in principle show thatthe sceptical arguments against the criterion are wrong.

This granted, the scenario is the following. You have basicbeliefs, and you cannot claim that you are justified in havingthem. But you cannot get rid of basic beliefs: insofar as you area human being, you have such a nature that there are thingsthat you cannot avoid believing. More precisely: if, in the caseof basic beliefs, having the impression that P is sufficient foryou to acquire the belief that P; and if, being alive, you cannotnot have the non-epistemic impressions that cause thosebeliefs, then, want it or not (i.e. judge the objects of theseimpressions of yours true or false or suspend your judgementabout them), you will have basic beliefs.

In other words, suspension of judgement is not effective onbasic beliefs. Even if, in virtue of the sceptic’s attack on hypoth-esizing, you suspend your judgement about their object (you do


not judge their object to be true), this will not prevent you fromhaving these beliefs. Indeed, basic beliefs are not the result of ajudgement – of a choice – you make, but they are directlycaused by non-epistemic impressions. Therefore, the sceptic’sarguments against hypotheses, which, if anything, produce yoursuspension of “judgement” on the objects of your basic beliefs,will not prevent you from having those beliefs.

Now, in this scenario, what would be reasonable for us todo: to accept that it is raining, without being capable to claimthat we are justified in doing so; or rather to suspend ourjudgement on the question whether it is raining? Since ourchoice is not free, it seems reasonable to believe that it is rain-ing. Yes, the sceptic arguments are correct: so what to do?What to do? There is nothing to do: for, whatever we will do,we will find ourselves in the same condition.

Thus, the “So what?” reply may enable the dogmatist towin over the sceptic. But there are reasons to think that thisvictory is limited. Let us suppose that the “So what?” reply, asfar as perceptual propositions are concerned, works – that thedogmatist rationally accepts that it is raining, despite the factthat he has no argument in favour of this claim. May this replybe used in order to produce an effective defence of – say – thefirst axiom of the Elements? In order for the reply to work, thecausal account of basic beliefs given above would have to bevalid not only for those beliefs which have simple perceptualstates of affairs as their object, but also for those which havethe first principles of sciences as their object; and it is not easyto see how first principles such as the above mentioned Euclid-ean axiom could cause us to believe them – or could cause any-thing else at all. We need some event (something which takesplace at a certain moment) to cause the impression, and thenthe belief, that P. The event is easy to find as far as my non-epistemic impression and my basic belief that it is raining areconcerned. But what about my belief that things which areequal to the same thing are also equal to one quather? What isthe event which is supposed to have caused this basic belief of

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mine, and when would it have taken place? I have no intelligi-ble answer to this question, and therefore – so far – I have toadjudicate the victory to the sceptic.

5. Scepticism and Platonic Hypothesizing

Do the sceptic objections and the dogmatic replies aboutbroad Aristotelian hypotheses, i.e. axioms, apply to Platonichypotheses? First of all, let me get clearer on what I mean hereby “Platonic hypotheses”. I do not mean to give a detailedaccount of that; I just want to sketch the basic idea of thehypothetical method as it is presented by Plato in Meno 86d-87d. Socrates and Meno are inquiring into the questionwhether virtue is teachable. Socrates suggests to attack thisquestion starting from a hypothesis (ejx uJpoqevsew"), followingthe contemporary geometrical practice:

S[ocrates]: “In the same way with regard to our question aboutvirtue, since we do not know either what it is or what kind ofthing it may be, we had best make use of a hypothesis in consider-ing whether it can be taught or not, as thus: what kind of thingmust virtue be in the class of mental properties, so as to be teach-able or not? In the first place, if it is different from or like knowl-edge, is it teachable or not – or, as we said just now, capable ofbeing recollected; but let it make no difference to us which termwe use – so, is it teachable? Or is this at least clear to everyone,that a man isn’t taught anything other than knowledge?” M[eno]:“I think so”. S: “But if virtue is some sort of knowledge, it’s clearthat it will be teachable”. M: “Of course”. S: “Then we havequickly finished with this point: if it is of one sort it is teachableand if of another, not”. M: “Certainly”. S: “Then, it seems, wemust consider what comes next, whether virtue is knowledge or itis different from knowledge”. M: “Yes, I think we should consid-er this after that” (Meno 87b-d)10.


10 For this passage I have used the translations of W.R.M. LAMB,

What does hypothesizing, in this passage, amount to? Youare making an inquiry: you have asked a question («Can virtuebe taught?»), and you are looking for an answer. In order tomake progress towards the answer, you venture some hypothe-sis – e.g. you suppose («for the sake of the argument») thatvirtue is a kind of knowledge. You next see whether, grantedthe hypothesis, you can answer the original question. If youcan, you proceed to worry about the hypothesis itself, askingwhether virtue is in fact a kind of knowledge.

In hypothesizing that virtue is a kind of knowledge, you donot commit yourself to the truth of that proposition, nor do youaccept that it is true. You may, of course, hope that it will turnout that your hypothesis is true. But, as a matter of fact, manyhypotheses will turn out to be false, and you will abandonthem: in doing so, you are not going back on anything you saidor changing your mind. Consider, by contrast, Aristotelianhypothesizing. In hypothesizing the first axiom of the Elements,you lay down, as a first principle, that proposition. In layingdown something as a first principle, you are thereby acceptingthat it is true; and if it emerges that the hypothesis is false, thenyou were mistaken and your hypothesizing was an error.

Platonic hypothesizing and Aristotelian hypothesizing,thus, have a common core, a different function, and some spe-cific features determined by their different function. Whenyou hypothesize that P, both in the Platonic and in the Aris-totelian case, you put forward (at least pro tempore) P, and youdo not argue for P nor produce any reason in its favour. But inthe Platonic case you are just considering the possibility that Pis true, and its consequences, without accepting that P is true;in the Aristotelian case you commit yourself to its truth.

The sceptic’s attack against hypothesizing, if it shows some-thing, shows that, whatever proposition you accept to be truewithout having any argument in its favour, you are not justified

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Plato. Meno, Harvard University Press, Cambridge (Mass.) 1924, andR.W. SHARPLES, Plato. Meno, Aris and Phillips, Warminster 1985.

in doing so. Therefore, this attack does not directly apply toyour Platonic hypotheses – to the propositions you just supposeto be true, without accepting them to be such. Nonetheless,when you platonically hypothesize that P, you do that for a rea-son – you suppose a certain proposition to be true in order tomake progress towards an answer to a question you have asked.Now if Agrippa’s modes are effective, so that you are not justi-fied in accepting anything as true, what would it be, for you, thepoint of supposing? The sceptic’s attack against the axioms, initself, does not threaten Platonic hypotheses. But the whole ofthe sceptical modes, which aims to produce suspension ofjudgement about any issue, seems to do that.

Now take Galen/Hume’s “So what?” reply to the hypo-thetical mode. The mode works: you cannot believe to be justi-fied in believing that P. «So what?» – is the reply – «I will stillbelieve that P: nature is too strong for me». If basic naturalbeliefs are directly caused by non-epistemic impressions with-out the intervention of judgement, then the sceptic’s mode isnot effective on them (so that you can ask: “So what?”), sincethese beliefs are not the result of a judgement – of a choice –you made. This strategy is maybe powerful enough to savesome Aristotelian hypotheses – those about simple perceptualfacts – from Sextus’ attack; but does it manage to save Platonichypotheses as well? When you hypothesize à la Platon, youmake a choice – you chose the proposition you want tohypothesize. On the other hand, when you hypothesize à laAristote on the externalist account (when you enjoy a basicbelief) you do not make any choice – you are just subject to apsychological state naturally caused by something (a fact,which causes in its turn a non-epistemic impression of yours).So if I ask you «Why do you Aristotelically hypothesize that itis raining?», you have a non-epistemic answer available – «Justby nature: I have had the pertinent impression, and I have no(free) choice!»; but if I ask you: «Why do you Platonicallyhypothesize that virtue is a kind of knowledge?», it seems thatsuch a non-epistemic explanation is not available – that you


have got to give me a reason, a belief (caused by a judgement)of yours, which explains your choice. Is it really so?

This question deserves a detailed scrutiny, which I cannotdevote myself to here. So in what remains I would like to showhow important such an issue may be for the sceptic. The ques-tion we have come to face is whether you can suppose some-thing without accepting/believing anything – i.e. whether asceptic can suppose something. And the act of supposing playsan important role in the sceptic’s treatment of dogmatic theses.Consider the arguments put forward by Sextus in his works.At least some of them are ad hominem: Sextus attempts toderive from certain dogmatic doctrines, using dogmatic rulesof inference, conclusions the dogmatists will not accept. Withhis argument on relativity in PH I 138, for example, Sextusproves that, given certain presuppositions common to ancientDogmatists, everything is relational. Now what is Sextus’ atti-tude towards the premisses and the inferential schema of hisad hominem arguments? Does he accept that their premissesare true, and the logical patterns they are instances of arevalid? Of course he does not. The ad hominem arguments areconstituted by premisses which only the dogmatist, by granti-ng them, is committed to. In putting forward arguments of thiskind, Sextus (the sceptic) does not commit himself to the truthof their premisses and of their conclusion, nor to their validity.He just considers the possibility for the premisses to be trueand the argument to be valid and shows that, if this is so, cer-tain conclusions follow. He (Platonically) hypothesizes; and hishypothesizing is essential in order for him to attack dogmatictheses by ad hominem arguments.

6. Conclusion

The term uJpovqesi" and its cognates, in Antiquity, denotetwo different acts. The first, which we have labelled “Aris-totelian hypothesizing”, is the act of laying down a proposition

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as a first principle or axiom of a science, which constitutes thestarting point of the demonstration of the theorems of that sci-ence. The second, which we have labelled “Platonic hypothe-sizing”, is the heuristic act of supposing something to be true(without accepting it to be true) in the course of an inquiry.Our main source for ancient Pyrrhonism, Sextus Empiricus,shows that the sceptic attacked the Aristotelian hypotheses,and made use of the Platonic hypotheses. The sceptic attackagainst Aristotelian hypotheses sounds successful. But theprice the sceptic has to pay in order to destroy them may betoo high; for, it may threaten not only the possibility, for thedogmatist, to lay down the axioms which found his science,but also the possibility, for the sceptic, to use Platonichypotheses in his ad hominem arguments against the dogma-tists.


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Scepticism and hypothetical method

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