What is a syllogism?

It came to my attention last week, that I often use a word in class that many people don’t have a clear understanding of . That word is ‘syllogism’. The word itself dates back to ancient Greece and is a combination of two parts – ‘syll-’ (derived from ‘syn-’ meaning ‘with’ or ‘together’ – for example, ‘syllable’, ‘syllabus’, ‘syllepsis’, ‘synthesis’, ‘synthetic’, ‘synoptic’, ‘syntactic’, etc) and ‘-logos’ (meaning ‘reason’, ‘word’, ‘idea’, ‘theory’ or ‘discourse’ eg ‘logic’, ‘psychology’, ‘geology’ (and almost any other science you care to name), ‘logocentric’, ‘logorrhoea’, etc.), so that the word ‘syllogism’, etymologically speaking, means a combination of distinct ideas. The word itself was first used by Aristotle in his Prior Analytics, which is also the source for the term ‘logic’.

For Aristotle, logic had two meanings: dialectic and analytic and it was the latter meaning which was understood in terms of syllogism. Aristotle’s theory of syllogism effectively defined the field of logic for over two thousand years. His key texts in logic were widely used during the Roman empire, but after the collapse of the empire in the 5th century AD, these texts were lost in the Latin Western Europe. However the texts were preserved in their original Greek in the Eastern Byzantine Empire and after the rise of Islam in the 8th century AD, many of these texts were translated into Arabic. The dispute between the Platonist Avecinna and the Aristotelian Averroes was an important stimulus to the development of medieval philosophy, especially the theology of Aquinas. It is only since the start of the 20th century that philosophers such as Frege, Russell, and Quine have discussed non-Aristotelian (syllogistic) forms of logic.

Despite its long history, a syllogism has a very precise meaning. It is the connection between two propositions (known as premises) which imply a conclusion. A classic example of a syllogism is as follows:

Socrates is a man

All men are mortal

Therefore, Socrates is mortal.

The first two propositions are the premises; the final proposition is the conclusion. The conclusion follows logically from the premises. In technical terms, the conclusion is deduced from the premises; and this deduction is indicated by the expression ‘therefore’.

There is much more that can be said about syllogism – its components and conditions, for example – but to understand that the relationship between the three propositions is a logical relationship (as against, say, a temporal relation – eg ‘This happened, and then that happened, and then something else happened’ as so often occurs in narrative or story telling – is to understand the key feature of the syllogism.


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