Aristotle - The Organon - index for ANALYTICA POSTERIORA Book 1 Part 10

Basic truths, peculiar (to a genus), and common (to all)

Paragraph 1 I call the basic truths of every genus those clements in it the existence of which cannot be proved.
Paragraph 2 Of the basic truths used in the demonstrative sciences some are peculiar to each science, and some are common, but common only in the sense of analogous, being of use only in so far as they fall within the genus constituting the province of the science in question.
Paragraph 3 Peculiar truths are, e.g. the definitions of line and straight;
Paragraph 4 That which expresses necessary self-grounded fact, and which we must necessarily believe, is distinct both from the hypotheses of a science and from illegitimate postulate - I say 'must believe', because all syllogism, and therefore a fortiori demonstration, is addressed not to the spoken word, but to the discourse within the soul, and though we can always raise objections to the spoken word, to the inward discourse we cannot always object.
Paragraph 5 The definition - viz. those which are not expressed as statements that anything is or is not - are not hypotheses:

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