To keep things relatively simple we confine our discussion to sentences of a formal language for which, again following Frege, denotation is simply a truth value. Both “there are infinitely many primes” and “there are infinitely many even numbers” agree on denotation—both are true—but clearly have different senses. All the basic ideas of Moschovakis are already present at the sentence level, though the ideas extend broadly. We quote from (Moschovakis 1994), on which our presentation is based.