PriorAnalytics successfully established a formal deduction system that could serve as an instrument for demonstrative science, or apodeiktikê epistêmê, as this is outlined in Posterior Analytics.
PriorAnalytics (esp. at A1-2, 4-7, 23, 45) is a proof-theoretic treatise in which Aristotle demonstrated certain of the logical relationships among syllogistic deduction rules.
This is especially evident at PriorAnalytics B2-4 where he systematically treated the various possibilities of valid arguments with combinations of true and false sentences as premises and conclusions in the three figures.
The Posterior Analytics is a text from Aristotle's Organon which treats of demonstration and of knowledge.
In the PriorAnalytics, syllogistic logic is considered in its formal aspect; in the Posterior it is considered in respect of its matter.
A syllogism which seems to be perfect both in matter and form, but which is not, is called sophistical, and these are dealt with in the book On Sophistical Refutations.