Consistency and inconsistency, in their logical sense, are relationships between statements or between the parts of a statement. They are not properties of reality as such.

“Wait,” you will say. “If consistency is not a property of reality, then you are implying that reality is not consistent. So reality is inconsistent?”

Not at all. Consistency and inconsistency are contraries, not contradictories, and they are properties of statements. So reality as such is neither consistent nor inconsistent, in the same way that sounds are neither white nor black.

We can however speak of consistency with respect to reality in an extended sense, just as we can speak of truth with respect to reality in an extended sense, even though truth refers first to things that are said or thought. In this way we can say that a thing is true insofar as it is capable of being known, and similarly we might say that reality is consistent, insofar as it is capable of being known by consistent claims, and incapable of being known by inconsistent claims. And reality indeed seems consistent in this way: I might know the weather if I say “it is raining,” or if I say, “it is not raining,” depending on conditions, but to say “it is both raining and not raining in the same way” is not a way of knowing the weather.

Consider the last point more precisely. Why can’t we use such statements to understand the world? The statement about the weather is rather different from statements like, “The normal color of the sky is not blue but rather green.” We know what it would be like for this to be the case. For example, we know what we would expect if it were the case. It cannot be used to understand the world in fact, because these expectations fail. But if they did not, we could use it to understand the world. Now consider instead the statement, “The sky is both blue and not blue in exactly the same way.” There is now no way to describe the expectations we would have if this were the case. It is not that we understand the situation and know that it does not apply, as with the claim about the color of the sky: rather, the situation described cannot be understood. It is literally unintelligible.

This also explains why we should not think of consistency as a property of reality in a primary sense. If it were, it would be like the color blue as a property of the sky. The sky is in fact blue, but we know what it would be like for it to be otherwise. We cannot equally say, “reality is in fact consistent, but we know what it would be like for it to be inconsistent.” Instead, the supposedly inconsistent situation is a situation that cannot be understood in the first place. Reality is thus consistent not in the primary sense but in a secondary sense, namely that it is rightly understood by consistent things.

But this also implies that we cannot push the secondary consistency of reality too far, in several ways and for several reasons.

First, while inconsistency as such does not contribute to our understanding of the world, a concrete inconsistent set of claims can help us understand the world, and in many situations better than any particular consistent set of claims that we might currently come up with. This was discussed in a previous post on consistency.

Second, we might respond to the above by pointing out that it is always possible in principle to formulate a consistent explanation of things which would be better than the inconsistent one. We might not currently be able to arrive at the consistent explanation, but it must exist.

But even this needs to be understood in a somewhat limited way. Any consistent explanation of things will necessarily be incomplete, which means that more complete explanations, whether consistent or inconsistent, will be possible. Consider for example these recent remarks of James Chastek on Gödel’s theorem:

1.) Given any formal system, let proposition (P) be this formula is unprovable in the system

2.) If P is provable, a contradiction occurs.

3.) Therefore, P is known to be unprovable.

4.) If P is known to be unprovable it is known to be true.

5.) Therefore, P is (a) unprovable in a system and (b) known to be true.

In the article linked by Chastek, John Lucas argues that this is a proof that the human mind is not a “mechanism,” since we can know to be true something that the mechanism will not able to prove.

But consider what happens if we simply take the “formal system” to be you, and “this formula is unprovable in the system” to mean “you cannot prove this statement to be true.” Is it true, or not? And can you prove it?

If you say that it is true but that you cannot prove it, the question is how you know that it is true. If you know by the above reasoning, then you have a syllogistic proof that it is true, and so it is false that you cannot prove it, and so it is false.

If you say that it is false, then you cannot prove it, because false things cannot be proven, and so it is true.

It is evident here that you can give no consistent response that you can know to be true; “it is true but I cannot know it to be true,” may be consistent, but obviously if it is true, you cannot know it to be true, and if it is false, you cannot know it to be true. What is really proven by Gödel’s theorem is not that the mind is not a “mechanism,” whatever that might be, but that any consistent account of arithmetic must be incomplete. And if any consistent account of arithmetic alone is incomplete, much  more must any consistent explanation of reality as a whole be incomplete. And among more complete explanations, there will be some inconsistent ones as well as consistent ones. Thus you might well improve any particular inconsistent position by adopting a consistent one, but you might again improve any particular consistent position by adopting an inconsistent one which is more complete.

The above has some relation to our discussion of the Liar Paradox. Someone might be tempted to give the same response to “tonk” and to “true”:

The problem with “tonk” is that it is defined in such a way as to have inconsistent implications. So the right answer is to abolish it. Just do not use that word. In the same way, “true” is defined in such a way that it has inconsistent implications. So the right answer is to abolish it. Just do not use that word.

We can in fact avoid drawing inconsistent conclusions using this method. The problem with the method is obvious, however. The word “tonk” does not actually exist, so there is no problem with abolishing it. It never contributed to our understanding of the world in the first place. But the word “true” does exist, and it contributes to our understanding of the world. To abolish it, then, would remove some inconsistency, but it would also remove part of our understanding of the world. We would be adopting a less complete but more consistent understanding of things.

Hilary Lawson discusses this response in Closure: A Story of Everything:

Russell and Tarski’s solution to self-referential paradox succeeds only by arbitrarily outlawing the paradox and thus provides no solution at all.

Some have claimed to have a formal, logical, solution to the paradoxes of self-reference. Since if these were successful the problems associated with the contemporary predicament and the Great Project could be solved forthwith, it is important to briefly examine them before proceeding further. The argument I shall put forward aims to demonstrate that these theories offer no satisfactory solution to the problem, and that they only appear to do so by obscuring the fact that they have defined their terms in such a way that the paradox is not so much avoided as outlawed.

The problems of self-reference that we have identified are analogous to the ancient liar paradox. The ancient liar paradox stated that ‘All Cretans are liars’ but was itself uttered by a Cretan thus making its meaning undecidable. A modern equivalent of this ancient paradox would be ‘This sentence is not true’, and the more general claim that we have already encountered: ‘there is no truth’. In each case the application of the claim to itself results in paradox.

The supposed solutions, Lawson says, are like the one suggested above: “Just do not use that word.” Thus he remarks on Tarski’s proposal:

Adopting Tarski’s hierarchy of languages one can formulate sentences that have the appearance of being self-referential. For example, a Tarskian version of ‘This sentence is not true’ would be:

(I) The sentence (I) is not true-in-L.

So Tarski’s argument runs, this sentence is both a true sentence of the language meta-L, and false in the language L, because it refers to itself and is therefore, according to the rules of Tarski’s logic and the hierarchy of languages, not properly formed. The hierarchy of languages apparently therefore enables self-referential sentences but avoids paradox.

More careful inspection however shows the manoeuvre to be engaged in a sleight of hand for the sentence as constructed only appears to be self-referential. It is a true sentence of the meta-language that makes an assertion of a sentence in L, but these are two different sentences – although they have superficially the same form. What makes them different is that the meaning of the predicate ‘is not true’ is different in each case. In the meta-language it applies the meta-language predicate ‘true’ to the object language, while in the object language it is not a predicate at all. As a consequence the sentence is not self-referential. Another way of expressing this point would be to consider the sentence in the meta-language. The sentence purports to be a true sentence in the meta-language, and applies the predicate ‘is not true’ to a sentence in L, not to a sentence in meta-L. Yet what is this sentence in L? It cannot be the same sentence for this is expressed in meta-L. The evasion becomes more apparent if we revise the example so that the sentence is more explicitly self-referential:

(I) The sentence (I) is not true-in-this-language.

Tarski’s proposal that no language is allowed to contain its own truth-predicate is precisely designed to make this example impossible. The hierarchy of languages succeeds therefore only by providing an account of truth which makes genuine self-reference impossible. It can hardly be regarded therefore as a solution to the paradox of self-reference, since if all that was required to solve the paradox was to ban it, this could have been done at the outset.

Someone might be tempted to conclude that we should say that reality is inconsistent after all. Since any consistent account of reality is incomplete, it must be that the complete account of reality is inconsistent: and so someone who understood reality completely, would do so by means of an inconsistent theory. And just as we said that reality is consistent, in a secondary sense, insofar as it is understood by consistent things, so in that situation, one would say that reality is inconsistent, in a secondary sense, because it is understood by inconsistent things.

The problem with this is that it falsely assumes that a complete and intelligible account of reality is possible. This is not possible largely for the same reasons that there cannot be a list of all true statements. And although we might understand things through an account which is in fact inconsistent, the inconsistency itself contributes nothing to our understanding, because the inconsistency is in itself unintelligible, just as we said about the statement that the sky is both blue and not blue in the same way.

We might ask whether we can at least give a consistent account superior to an account which includes the inconsistencies resulting from the use of “truth.” This might very well be possible, but it appears to me that no one has actually done so. This is actually one of Lawson’s intentions with his book, but I would assert that his project fails overall, despite potentially making some real contributions. The reader is nonetheless welcome to investigate for themselves.