Universal instantiation

Universal instantiation is something used in logic, which is a way of reasoning. It is a way of using facts that you know to figure out other facts. It is like using a puzzle, where one clue leads to the next one.

With universal instantiation, you start with a fact that looks like this:

For all things x, if x has the property P, then x has the property Q.

Universal instantiation says that if you have one example of something x that has the property P, then you know that it must also have property Q.

For example, let's say that P = "has four legs" and Q = "is an animal". This means that for all things x, if x has four legs then it must be an animal.

Now, let's say that we have one example of something x – say, a dog. We know that a dog has four legs.

Using universal instantiation, we can then say that this dog must also be an animal.