March 5, 2018

## A modest theory of truth

I have previously discussed some of the problems that I have with the so-called correspondence theory of truth.  In this post, I shall suggest my own theory.

I am describing it as modest, because it does not attempt to settle all truth questions.  The use of “true” in ordinary language is a mess, and my theory will not attempt to address all such use.  Rather, it is intended only for technical uses, such as in mathematics and science.

In my last post, I made a distinction between ordinary mathematical statements such as $3+5=8$ and the axiom systems (such as the Peano axioms)  that we use to prove those ordinary statements.  There is widespread agreement on truth questions about those ordinary mathematical questions.  But there is less agreement about whether axioms are true.  Mathematics can be done, without settling questions on the truth of the axioms used.

Coming up with axiom systems is also part of mathematics.  But when a new axiom system is offered, the main concern is on whether that axiom system is useful.  Whether the axioms are true is often not asked, perhaps because there isn’t a good way to decide.  Axiom systems are usually adopted on a pragmatic basis.  That is, they are adopted for their usefulness.

Something similar happens in science.  The ideal gas laws of physics are a good example.  Those laws are true only for an imagined ideal gas.  They are false for any real gas.  But although technically false, they provide a pretty good approximation of the behavior of real gases.  And that makes them very useful.  So, with the gas laws, we see important scientific laws that are adopted on a pragmatic basis, even though they might be technically false.

February 26, 2018

## Mathematical truth

While this post is about mathematical truth, it is really intended as part of a series of posts about truth.  The mathematics here will be light.  I am choosing to discuss mathematical truth because some of the distinctions are clearer in mathematics.  But I do intend it to illustrate ideas about truth that are not confined to mathematics.

Mathematicians actually disagree about mathematical truth.  But the disagreements are mostly peripheral to what they do as mathematicians.  So they usually don’t get into intense arguments about these disagreements.

### Philosophy

First a little philosophical background.

There is a school of mathematics known as Intuitionism.  This differs from the more common classical mathematics, in that it has a more restrictive view of what is allowed in a mathematical proof.  And, consequently, it has a more restrictive view of truth.  In particular, Intuitionists do not accept Cantor’s set theory.

The mainstream alternative to Intuitionism is usually called “Classical Mathematics“.

This post mainly has to do with truth in classical mathematics.  I mention Inuitionism just to acknowledge its existence and indicate that it is not what I will be discussing.

February 20, 2018

## What is truth?

Pilate famously asked the title question (John 18:38).  I expect people have been asking that question for as long as they have been asking questions.  For a good discussion of theories of truth, check the entry in the Stanford Encyclopedia of Philosophy.

Truth is a central concept in philosophy.  But I am not at all satisfied with the way that it is used.  Hence this post.

### Correspondence

If you ask about truth, you may be answered with the correspondence theory.  But the idea of “correspondence” is usually left unexplained.  I sometimes see statements similar to:

• A sentence is true if it corresponds to the facts.
• A sentence is true if it expresses what is the case.
• A sentence is true if it expresses the state of affairs.

The trouble with all of these, is that they seem to be roundabout ways of saying “A sentence is true if it is true.”  And that does not say anything at all.