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Texte à méditer :  La raison du plus fort est toujours la meilleure.
  
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Hors des sentiers battus
La vérité-cohérence

  "We may now proceed to formulate the coherence-theory afresh in the following terms. Truth in its essential nature is that systematic coherence which is the character of a significant whole. A “significant whole” is an organized individual experience, self-fulfilling and self-fulfilled. Its organization is the process of its self-fulfilment, and the concrete manifestation of its individuality. But this process is no mere surface-play between static parts within the whole; nor is the individuality of the whole, except in the movement which is its manifestation. The whole is not, if “is” implies that its nature is a finished product prior or posterior to the process, or in any sense apart from it. And the whole has no parts, if “to have parts” means to consist of fixed and determinate constitutents, from and to which the actions and interactions of its organic life proceed, much as a train may travel backwards and forwards between the terminal stations. Its “parts” are through and through in the process and constituted by it. They are “moments” in the self-fulfilling process which is the individuality of the whole. And the individuality of the whole is both the pre-supposition of the distinctive being of its “moments” or parts and the resultant which emerges as their co-operation, or which they make and continuously sustain.
  It is this process of self-fulfilment which is truth, and it is this which the theory means by “systematic coherence.” The process is not a movement playing between static elements, but the very substance of the moving elements. And the coherence is no abstract from imposed upon the surface of materials, which retain in their depths a nature untouched by the imposition. The coherence—if we call it a “form”—is a form which through and through inter-penetrates its materials; and they—if we call them “materials”—are materials, which retain no inner privacy for themselves in independence of the form. They hold their distinctive being in and through, and not in sheer defiance of, their identical form; and its identity is the concrete sameness of different materials. The materials are only as moments in the process which is the continuous emergence of the coherence. And the form is only as the sustained process of self-fulfilment, wherein just these materials reveal themselves as constitutive moments of the coherence.

  In the above formulation I have endeavoured to express the coherence-notion so as to emphasize the concreteness of the coherence which is truth, as against the view which found truth in formal consistency; and I have insisted upon the conception of truth as a living and moving whole, as against the Cartesian view of fixed truths on which the structure of knowledge is built."

 

Harold H. Joachim, The Nature of Truth, 1906, Oxford Clarendon Press, in Simon Blackburn and Keith Simmons, Truth, Oxford University Press, 1999, p. 50-51.



  "Beaucoup de philosophes ont tenté de trouver une définition de la vérité qui ne consiste pas en une relation de la pensée à autre chose. La tentative la plus intéressante faite en ce sens est la théorie de la vérité « cohérence ». On affirme alors que la marque du faux, c'est de ne pas être en accord avec nos croyances, tandis que l'essence de la vérité réside dans le fait de trouver sa place dans le système parfaitement clos de la Vérité.
  Cette conception bute pourtant sur une, ou plutôt deux, difficultés majeures. La première est qu'il n'y a aucune raison de penser qu'un seul système cohérent de croyances est concevable. Peut-être un romancier doué de l'imagination nécessaire pourrait-il réinventer le passé du monde tant et si bien que ce passé, quoique entièrement fictif, s'ajusterait parfaitement à ce que nous savons. Dans un domaine plus scientifique, il arrive souvent que deux ou plusieurs hypothèses soient également capables de rendre compte de tous les faits connus sur une question ; et malgré l'effort des scientifiques pour découvrir un fait qui puisse disqualifier toutes les hypothèses sauf une, rien n'assure qu'ils puissent toujours y parvenir.

  Il n'est pas rare, en philosophie aussi, que deux hypothèses rivales soient également capables de rendre compte de tous les faits. Il est ainsi possible que la vie ne soit qu'un songe, que le monde extérieur ait tout juste la réalité des événements du rêve ; mais bien que cette conception ne soit pas contradictoire avec les faits connus, il n'y a pas de raison de la préférer à celle du sens commun, pour qui les choses et les gens existent réellement. Bref, la définition de la vérité par la cohérence échoue devant l'absence de preuve qu'un seul système cohérent soit possible.
  L'autre objection contre cette définition de la vérité est qu'elle présuppose qu'on a donné un sens au terme « cohérence », alors que ce terme renvoie à la vérité des lois logiques. Deux propositions sont cohérentes quand elles peuvent être vraies ensemble, incohérentes quand l'une au moins doit être fausse. Or pour savoir si deux propositions peuvent être vraies ensemble, nous devons connaître certaines vérités comme la loi de non-contradiction. Par exemple, les deux propositions « cet arbre est un hêtre », et « cet arbre n'est pas un hêtre », ne sont pas cohérentes, selon la loi de non-contradiction. Mais si la loi de non-contradiction elle-même était soumise à ce test de cohérence, nous trouverions, si nous choisissions de la répudier comme fausse, que plus rien ne peut être incohérent avec quoi que ce soit. Si bien que les lois logiques, parce qu'elles fournissent l'ossature ou le cadre à l'intérieur duquel prend sens le test de la cohérence, ne peuvent être elles-mêmes établies à travers ce test.
  Pour ces deux raisons, on ne peut accepter l'idée que la cohérence constitue la signification de la vérité, même si souvent la cohérence est un critère très important de la vérité, une fois que tout un savoir a déjà été constitué."

 

Bertrand Russell, Problèmes de philosophie, 1912, Chapitre XII, tr. fr. François Rivenc, Payot, 1989, p. 145-147.

 

  "Many philosophers have been led to try to find some definition of truth which shall not consist in relation to something wholly outside belief. The most important attempt at a definition of this sort is the theory that truth consists in coherence. It is said that the mark of falsehood is failure to cohere in the body of our beliefs, and that it is the essence of a truth to form part of the completely rounded system which is The Truth.
  There is, however, a great difficulty in this view, or rather two great difficulties. The first is that there is no reason to suppose that only one coherent body of beliefs is possible. It may be that, with sufficient imagination, a novelist might invent a past for the world that would perfectly fit on to what we know, and yet be quite different from the real past. In more scientific matters, it is certain that there are often two or more hypotheses which account for all the known facts on some subject, and although, in such cases, men of science endeavour to find facts which will rule out all the hypotheses except one, there is no reason why they should always succeed.

  In philosophy, again, it seems not uncommon for two rival hypotheses to be both able to account for all the facts. Thus, for example, it is possible that life is one long dream, and that the outer world has only that degree of reality that the objects of dreams have; but although such a view does not seem inconsistent with known facts, there is no reason to prefer it to the common-sense view, according to which other people and things do really exist. Thus coherence as the definition of truth fails because there is no proof that there can be only one coherent system.
  The other objection to this definition of truth is that it assumes the meaning of 'coherence' known, whereas, in fact, 'coherence' presupposes the truth of the laws of logic. Two propositions are coherent when both may be true, and are incoherent when one at least must be false. Now in order to know whether two propositions can both be true, we must know such truths as the law of contradiction. For example, the two propositions, 'this tree is a beech' and 'this tree is not a beech', are not coherent, because of the law of contradiction. But if the law of contradiction itself were subjected to the test of coherence, we should find that, if we choose to suppose it false, nothing will any longer be incoherent with anything else. Thus the laws of logic supply the skeleton or framework within which the test of coherence applies, and they themselves cannot be established by this test.
  For the above two reasons, coherence cannot be accepted as giving the meaning of truth, though it is often a most important test of truth after a certain amount of truth has become known."

 

Bertrand Russell, The Problems of philosophy, 1912, Chapter XII, Dover Publications Inc., 1999, p. 88-89.

 

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