In an earlier post post I reviewed the mathematical significance of Tarski’s definition of truth and promised that I would explain why it is philosophically useless in a later post. I wasn’t sure anyone was interested and never got around to making that post but thanks to a comment I’ve finally gotten around to this post.

Briefly Tarski’s ‘defines’ truth by endorsing the following scheme (called the T-schema) for every sentence S:

‘S is true’ if and only if S

To take the canonical example:

“‘Snow is white’ is true” if and only if ‘Snow is white’

Now I don’t dispute that this scheme indeed holds (perhaps even necessarily) for the concept truth. I’m even willing to grant that this scheme may ‘define’ truth in some sense but what I dispute is that it tells us anything significant about truth.

Although we normally expect a definition to explain¹ the concept in question not all definitions do so. For instance consider the definition of a ‘good action’ as “an action one morally ought to take.” While such a definition might explain the term ‘good action’ to someone who didn’t speak the language or help organize a philosophical theory in no way could it be said to explain what a good action was or give us a grip on the nature of morality. That is the definition merely reveals trivial linguistic connections between words that all make use of the same underlying opaque concept.

Tarski’s definition of truth is just the same. Sure if one didn’t know how to translate the English word ‘true’ into German communicating the T-schema in English could help your listener realize that ‘wahr’ was the correct translation. However, the T-schema only manages this by bootstrapping off the fact that your listener already understands assertability in English. In other words all the T-schema expresses is the connection between the predicate ‘true’ and assertability. In order to find the fact that “‘Snow is white’ is true” if and only if ‘Snow is white’ enlightening you must already understand what it means for snow to be white. If you don’t see this just imagine a linguistic practice where uttering ‘Snow is white’ conveyed your disbelief in the whiteness of snow. In that case the the word defined by the T-schema would have the same meaning as our word ‘false’.

When philosophers ask “What is truth?” they don’t want to know when they should term a sentence ‘true’ supposing they already know when to endorse it as fact. Rather they want to know what it means to assert something as fact, e.g., what is the relationship between ‘Snow is white’ and the external world. Tarski’s ‘definition’ of truth does nothing to explain truth in this sense, it is up to other theories like the correspondence theory of truth to answer this question. The T-schema (in a philosophical context) only illustrates the obvious and trivial relationship between asserting a sentence and asserting that sentence is true. As I outlined in my previous post on the subject Tarski’s definition of truth is a substantial mathematical contribution but it just doesn’t cut much philosophical ice.

Note that nothing I’ve said here conflicts with the deflationist position that the T-schema is the only thing that can be cogently said about truth. I actually find this position quite appealing but the substance of this view is not that the T-schema says something substantial about truth but that there isn’t anything substantial to say about truth. Intuitively this seems right because you must already understand what it means to assert things to even make sense of any other proposal but I haven’t thought about it enough to be totally convinced.