New posts in First Order Logic

Decidability and "truth value"

What happens if the empty set is not a subset of every set?

If $\Gamma$ is consistent and $\Gamma\not\vdash\phi$, then $\Gamma\cup\{\neg\phi\}$ is also consistent. Why?

Writing predicates - is the quantifier necessary?

Why do first order languages have at most countably many symbols?

In what sense is propositional logic "zeroth-order logic?"

First-order sentence involving only a symmetric binary relation with only infinite models

Proof of Decidability of Monadic First Order Logic

What will be the negation of this statement:

uniformity in quantifier elimination