Pons asinorum (Latin ‘asses’ bridge’), a methodological device based upon Aristotle’s description of the ways in which one finds a suitable middle term to demonstrate categorical propositions. Thus, to prove the universal affirmative, one should consider the characters that entail the predicate P and the characters entailed by the subject S. If we find in the two groups of characters a common member, we can use it as a middle term in the syllogistic proof of (say) ‘All S are P’. Take ‘All men are mortal’ as the contemplated conclusion. We find that ‘organism’ is among the characters entailing the predicate ‘mortal’ and is also found in the group of characters entailed by the subject ‘men’, and thus it may be used in a syllogistic proof of ‘All men are mortal’. To prove negative propositions we must, in addition, consider characters incompatible with the predicate, or incompatible with the subject. Finally, proofs of particular propositions require considering characters that entail the subject. See also SYL- LOGIS. I.Bo.