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What is truth? An absurd question?

Philosophers are seekers of truth. They are supposed to love wisdom and, by extension, love truth. It seems only logical that any philosopher should ask the question, What is truth? Surprisingly, Kant argues that this question might not even make sense in the first place.

In The Critique of Pure Reason, Kant tackles the problem of truth in the third section of his Introduction to Transcendental Logic, titled “On the Division of General Logic into Analytic and Dialectic”. His conclusion: there is no universal and sufficient criterion of truth because such a criterion is inherently contradictory.

The sceptics’ challenge

Kant wants to critique the sceptics who used to challenge logicians by demanding, “What is truth?” The logicians of Kant's time studied Aristotle's Organon, in which Aristotle exposed his system of formal logic. This logic studies the correctness of thinking and uses true and false propositions. Because logicians constantly talk about true propositions, the sceptics were incited to tease them by asking what truth is. What the sceptics are really asking for is a touchstone we could apply to any knowledge claim to determine if it’s true. 

The nominal definition of truth

Kant’s starting point is a nominal definition of truth. A nominal definition is a definition of a name and not of the thing itself. A nominal definition clarifies a term rather than provides the essence of it. Kant’s nominal definition of truth is “the accordance of knowledge with its object”. This definition is derived from the definition attributed to Isaac Israeli. Isaac Israeli defines truth as the adequacy of understanding and reality (adequatio intellectus et rei). This definition seems to do the job. Take, for example, the judgement "Socrates is a man" is true if Socrates really was a man. This means that the object “Socrates” and the knowledge "Socrates is a man" agree with each other. This definition also filters out false statements. The knowledge “Socrates is a woman” is not in accordance with the object and thus is false. So far, so good.

So what’s the problem? Definition doesn’t actually help us identify what is true. Why? Because in order to determine whether a judgement agrees with its object, we already need to know what the object is and whether our judgement fits it. I cannot use this nominal definition to recognise the truth of any proposition which I do not know to be true. I am not a sports fan; I do not know who won the 2010 football World Cup. If someone were to provide me with this nominal definition of truth and the sentence “Spain won the 2010 World Cup”, then I would have no way of knowing whether this is true or false. A nominal definition of truth is of no use. 

What Kant actually wants to show is that this question is absurd and outrageous. When logicians try to define truth, they fall into a diallel. A diallel is a logical fallacy in which a proposition is proved by a second proposition, while the second proposition is proved by the first. For example, given two propositions, A and B, a diallel takes the following form: if A is true, then B is true, and if B is true, A is true. Any attempt to define truth ends in a “ridiculous spectacle”, because a definition of truth supposes the truth of the definition.

A universal criterion of truth

Kant wants to further show the absurdity of the question by demonstrating that a universal criterion of truth with respect to content (or “matter”) is contradictory in itself. Take, for example, the statement “Socrates is a man.” The truth of this statement depends on the object, “Socrates”. If we’re referring to a cat named Socrates, the statement is false. If we’re referring to the Greek philosopher, it’s true. Truth depends on the content of the statement and on the specific object it references.

The problem is that a universal criterion of truth would have to apply to any statement, regardless of their content. This is impossible because truth necessarily involves a relationship to specific content. A universal mark would require abstracting from all content—but truth is about content. If we remove the content from “Socrates is a man”, we are left with “x is a y”. This proposition can not be true or false. Truth disappears with the content.

A necessary criterion of truth

Kant has established that a universal criterion of truth is impossible, but what about a necessary criterion? This is possible! Such a criterion is not able to tell us when something is true; rather, it will provide necessary rules to which truth must abide. According to Kant, formal logic is a necessary criterion of truth. Logic, as described in Aristotle’s Organon, outlines the structure of reasoning without its content. This logic can determine whether a conclusion follows necessarily from its premises. It is possible to determine if a syllogism is valid or not based on its form alone.

For example:

  1. All humans are mortal.

  2. Socrates is a human.

  3. Therefore, Socrates is mortal.

This syllogism is valid. Logic, however, can not say whether the conclusion of this syllogism is true, as that depends on the content. Logical rules are a universal criterion of truth: if a judgement violates these rules, it is false. Logic gives a necessary condition for truth, but not a sufficient one. A judgement can be logically valid and still be false if its premises are untrue.

Take this example:

  1. All humans are immortal.

  2. Socrates is a human.

  3. Therefore, Socrates is mortal.

This argument is valid but false. Formal logic gives us a negative criterion of truth—it can tell us when something is false (because it contradicts the rules of logic), but it can not tell us what is true. It’s a "conditio sine qua non" of knowledge; this means that without this condition, knowledge cannot be true, but not a guarantee of truth.

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