What constitutes a "legitimate" first order sentence

[Graeme Humphrey]

I'm having an issue finding the definition of what what a valid first
order sentence is.

I see examples that don't make sense but does that make them
illegitimate?

E.G. ¬IsDog(x) ^ IsDogLabrador(x)

So there are two issues with this. The first is it will never
evaluated to true, and secondly is it legitimate to evaluate a non-dog
in a function for a dog.

However syntax is correct so does that make it illegitimate?

Any help appreciated,
Thanks

[Raf]

I think that your example is a valid first order sentence (i.e it is syntattically correct).

The fact that (in our world) it could never be true does not make it invalid, but only unsatisfiable.

My two cents.

Bye

Raf

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