May 9, 2021

## Truth in ordinary life

Last week, I posted about truth in mathematics. So now I want to move to discussing our use of “true” in every day life.

## Ordinary statements

As with mathematics, there are many statements on which people can agree as to their truth. These are typically simple descriptive statements such as “it is raining” or “the grass need mowing” or “there’s a pothole down the street.” These are the kinds of statements that we can check for ourselves by looking around. There are others that we cannot quite check for ourselves, such as “the Yankees won today’s baseball game”, but we generally accept the rulings of the umpires or other officials. The statement “Biden won the presidential election” should be of this type, though there is surprising disagreement this time around.

For these types of statements, we judge their truth based on our ordinary language use, including the meanings of the words. We can perhaps say that they are true because they follow to implicit rules of language use, or the implicit conventions of language use. For such statements, truth is usually not controversial because of the shared agreement about these implicit rules.

## Heliocentrism

There are other statements which have generated disagreement. A traditional example is the question of whether heliocentrism is true. Galileo got into an argument with the church because of his insistence on heliocentrism. Today, most people accept heliocentrism without much disagreement. Clearly this is a different kind of question from those I considered to be ordinary statements.

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May 3, 2021

## Truth in mathematics

I’m tentatively planning several posts on “truth”, and mathematics seems a good place to start — partly because I’m a mathematician, and partly because some of the distinctions seem clearer in mathematics than in other areas.

I can think of at least two different ways that we use “true” in mathematics. The most basic of these is with ordinary statements such as $2+2=4$ or the Pythagorean theorem. Both are generally recognized as true. The other way that some people use “true” is when they talk about whether the axioms are true. That could refer to the Peano axioms for arithmetic, the Zermelo-Fraenkel or about whether the axiom of choice is true or about whether the continuum hypothesis is true. As we shall discuss below, the way we think about the truth of axioms is different from the way that we think about the truth or ordinary mathematical statements.

## Ordinary statements

When I talk of “ordinary statements” in mathematics, I am talking about statements such as $2+2=4$ in arithmetic or the Pythagorean theorem in geometry. We normally have a system of axioms that we use in our mathematics. For ordinary arithmetic, these are the Peano axioms. For geometric questions, we normally use Euclid’s axioms, supplemented by some version of the parallel postulate. For set theory, we most commonly use the Zermelo-Fraenkel axioms, possibly supplemented by the axiom of choice.

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June 20, 2018

## Crossword puzzles

This post is not about how to solve a crossword puzzle.  It’s about what we can learn about truth by looking at those puzzles.

Let’s suppose that you have been working on a crossword puzzle.  And you think you have it solved.  So how can you tell whether you have the correct solution?  That is the question that I wish to examine.  And since “correct” is closely related to “true”, it is a question about truth.

### Sudoku puzzles

Before looking more closely at crossword puzzles, let’s take a quick peek at Sudoku puzzles.  They make a good contrast with crossword puzzles.

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June 3, 2018

## Truth and reference

I recently posted this in a comment on another blog:

We cannot just take a sentence and ask if it is true. We first have to inquire about everything referenced by that sentence. If people don’t agree on the references, they won’t agree on the truth of the sentence.

It’s a rather obvious point.  Yet it is often overlooked.

Earlier this year, I proposed a modest theory of truth, in which I suggested that we judge the truth of a sentence based on whether it conforms with standards.  What I mainly had in mind, and what my example illustrated, were the standards that we follow for settling questions of reference.  Likewise, my posts about carving up the world are really all about how we go about finding ways to reference parts of the world.

### Consciousness

In a way, the problems of consciousness are also closely connected with reference.  The so called “hard problem” arose because people thinking about AI (artificial intelligence) did not see how a computer could possibly be conscious.  Well, of course it cannot be conscious.  For to be conscious is to be conscious of something, to be conscious of a world.  Consciousness depends on reference.  Or, as philosophers usually say that, it depends on intentionality.

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March 28, 2018

## Saying true things about the world

This continues my series of posts on truth.  Up to now, my discussion has mainly been technical.  But truth matters to us because we want to be able to say true things.  We use natural language statements about the world (where “world” is understood broadly) in order to say those true things.

Linguistics is not my area, but I cannot avoid it completely.  Chomsky’s linguistics is based on the idea that language is a syntactic structure.  Presumably the semantics are an add-on to that underlying syntactic structure, although Chomsky doesn’t say much about how semantics makes it into language.

I very much disagree with Chomsky’s view of language.  As I see it, language is primarily semantic.  I see the rules of syntax as mostly an ad hoc protocol used for disambiguation.  So today’s post will be mainly about semantics or meanings.  This has to do with how words can refer to things in the world, or how words can be about something.  This is related to the philosophical problem of intentionality (or aboutness) of language statements.  Here I will be presenting only a broad overview.  I expect to get into more details in future posts.

### Carving up the world

I hinted at the idea when I presented my modest theory of truth.  There, I said:

Similarly, if I were to say “the cat is on the mat”, you would see that as true provided that I had followed the standards of the linguistic community in the way that I used the words “cat”, “on” and “mat”.

According to my theory of truth, we need standards for the use of words such as “cat”, “on” and “mat”, and we judge the truth of a statement based on whether it conforms to those standards.

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March 21, 2018

## Truth and pragmatics

We make decisions.  That’s a good part of what we do.  For example, I have just decided to compose a post about decision making.

But how do we make decisions?  How do we decide?

Generally speaking, we make some decisions on the basis of what is true.  And we make other decisions on the basis of what works best for us.  That latter kind of decision is usually said to be a pragmatic choice.

### Examples

If I am solving a mathematical problem such as balancing my checkbook, then I am making decisions based on truth.  If I am working on a logic problem, again that is going to be making decisions based on truth.

I walk into a restaurant, look at the menu, and decide what to order.  That’s normally a pragmatic choice.  It need not be.  Perhaps I have created a rule for myself that if it is Sunday I should order the first item on the menu, if it is Monday I should order the second item, etc.  If I am exactly following those rules, then I am making a decision based on truth.  But that isn’t what we normally do when ordering a meal at a restaurant.

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March 11, 2018

## Odds and ends about truth

In my previous post, I proposed a somewhat limited theory of truth.  Here I’ll discuss some of the issues that might arise out of that theory.

### What if there are no relevant standards?

According to my theory, we assess the truth of a statement based on accepted standards for evaluating that truth.  So what will happen if there are no applicable standards?

The simple answer, is that we cannot assess the truth of that statement.

This is not really a new situation.  When Gödel proved his incompleteness theorem, he showed that there are mathematical statements (arithmetic statements) cannot be proved true or false.  Such statements are often said to be undecidable.  If you use my suggested theory of truth, then there will  be undecidable statements in ordinary life, and not just in mathematics.

The existence of undecidable statement has not been any kind of calamity in mathematics.  And it is unlikely to pose a serious problem in ordinary life.

### What about the law of the excluded middle?

According the the law of the excluded middle (or LEM), a statement is either true or false.  However, LEM is usually considered a law or reasoning, rather than part of a theory of truth.  Mathematicians still use LEM in their reasoning, following Gödel’s incompleteness theorem.  And it does appear to cause any problems.  I would expect the same to be true in ordinary life.  If you use my suggested theory of truth, you will not have to give up LEM as part of your reasoning strategy.

### Changing standards

What happens if we change standards?

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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.

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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.

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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.

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