Section Progress:

2.4  Necessary vs. Contingent

Consider the sentence "Pia is innocent."

Logic truths are necessarily true, and logical falsehoods are necessarily false.

But the claim that Pia is innocent isn't necessarily true or false. It is just a plain old truth or falsity.

Logic doesn't make it true or false. Pia's actions make it true or false.

Contingent: Something that might or might not be the case, from a logical point of view; not necessary.

The opposite of necessary is contingent, which is what that sentence is.

Most of the things we talk about in everyday life are contingent:

  • "It is raining."
  • "There is no life on the moon."
  • "The economy grew by 2% last year."

We've been focusing on special cases of validity, which require you to understand logical truth and falsehood.

The point of this section is to balance the narrative: don't start thinking that everything is just a matter of logic.

Most sentences happen to be true or false depending on how the world is, like those listed above.

Let's practice using these concepts.

It will also help  your understanding to realize that there are different types of necessity. "Necessary" means something must be the case relative to a set of laws, principles, or rules.

For example, physical necessity means something must be true because of the laws of physics.

Logical necessity means something must be true because of the laws of logic.

Those two things are not the same. The laws of physics, such as gravity or the speed of light, were probably formed in the first milliseconds after the big bang. From a logical point of view, had things gone slightly differently, we might have different laws governing the physical universe.

Since this is a logic course and not a physics course, when we talk about necessary truth, you can assume we are talking about logical laws, not physical laws or moral laws or anything else.

That's why we will move interchangeably between talk of logical truth and necessary truth, and logical falsehood and necessary falsehood.

2.4 Necessary vs. Contingent