Aristotle’s philosophy of logic

When Aristotle was born in 384 BC, logic was in its infancy and indistinguishable from rhetoric; the ancient Greeks viewed rhetoric as useful because it could help them secure a business deal or win a case in court. The purpose of rhetoric was to win; logic (even twisted logic) was just part of its arsenal.

Aristotle came up with a fresh approach to logic. His books “Categories,” “Prior Analytics” and “Posterior Analytics” give us his insights in this regard.

“Categories” was written around 350 BC. Aristotle was just thirty-four years old at that time. The book enumerates crucial categories for analysing reality.

The Aristotelian categories refer to substances, qualities and quantities, and to the relations between objects. They don’t add much to terms used by prior philosophers such as Plato (428-347 BC), Anaxagoras (500-428 BC) or Democritus (460-370 BC), but for the first time, they provide a systematic overview.

The categories in Aristotle’s philosophy of logic

In “Categories,” Aristotle introduces the term “substance.” I must point out that he did not mean “material” or “ingredient” as we do nowadays.

For Aristotle, “substance” means “entity,” “creature” or key characteristics that define them. He says for instance that “the substance of human beings is rationality.” He means that the key characteristic that defines humans is rationality.

Aristotle’ second and third works on logic are titled “Prior Analytics” and “Posterior Analytics.” They contain much more innovative ideas than “Categories.” Aristotle must have written “Prior Analytics” and “Posterior Analytics” after Plato’s death, that is, after 347 BC.

Those two works are devoted to syllogistic reasoning, that is, to the rules for drawing correct conclusions from facts or statements.

Syllogisms in Aristotle’s philosophy of logic

The term “syllogism” employed by Aristotle simply means a logical argument; every syllogism is composed of three steps of which the initial two are called premises (major premise and minor premise); the third step is the conclusion.

Here is an example of a syllogism. “All men are mortal” is the major premise, and “Achilles is a man,” the minor premise. If you combine the major and the minor premise, you’ll arrive at the conclusion “Achilles is mortal.”

In this example, “Achilles is a man” is the minor premise because Achilles is included in the major premise “All men are mortal.” Since Achilles is a man, he must be mortal.

“Prior Analytics” teaches us that conclusions must be either true or false. Either Achilles is a man or he is not. If he is, then he must be mortal; when syllogisms are well-constructed, there is no possibility of a middle ground. Achilles cannot be at the same time mortal and immortal. He is either one or the other.

The rejection of contradictions in Aristotle’s philosophy of logic

In addition, “Prior Analytics” teaches that conclusions must be consistent with the facts and with other conclusions. If there are contradictions, something is wrong. Contradictions imply a mistake in the facts, in the conclusion, or in both.

Why should we reject contradictions? Because every aspect of reality is consistent with reality as a whole. The universe is hundred per cent aligned, even if we sometimes lack enough information to draw the right conclusion.

“Posterior Analytics” presents different types of syllogisms based on the quantity and quality of the premises. For instance, universal propositions apply to all members of a certain group, while particular propositions apply only to some members, and singular propositions apply only to one individual.

Furthermore, qualitative propositions can affirm or deny the existence of connections between two terms. If they affirm the connection, they are called “positive propositions; ” and if they deny the connection, they are called “negative propositions.”

In “Posterior Analytics,” Aristotle enumerates twenty-four different types of syllogisms. Each type embodies a different relationship between the premises. Syllogism types arise from applying the “Categories” to the general concept of syllogism.

The concept of “middle term” in Aristotle’s philosophy of logic

Syllogisms (and logic as a whole) only work when premises are connected by a middle term, that is, by a shared attribute. I have used the example “All men are mortal” and “Achilles is a man.” The concept “man” is the middle term that is connecting the major and minor premises.

In the absence of a middle term, the premises won’t overlap and no conclusion can be drawn. If I enunciate “All men are mortal” and “Achilles is tired,” the premises are unconnected. I would then have to argue that “all creatures that get tired are mortal” in order to establish a logical connection.

Unfortunately, countless people nowadays have abandoned Aristotelian logic and embraced superstition. As a result, their lives are driven by fear, not by purpose; their actions contradict each other because they lack integration; their mistakes worsen as time goes by and will eventually lead to disaster.

If you are interested in applying Aristotelian philosophy in daily life, I recommend you my book titled “The 10 principles of rational living.”

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