How does predicate logic handle contradictory statements about something that does not exist? Let * **p** denote _ringing telephone_ * _**s_** denote _someone_ * **A** denote _answered_ 1. ¬∃x(Px) 2. ∀x∃y((Px⋀Sy) →Ayx) 3. ∀x¬∃y((Px⋀Sy) →Ayx) So, 1. There are no ringing telephones. 2. Every ringing telephone was answered by someone. 3. Every ringing telephone was not answered by someone. Those three statements could all be true. (I believe 'vacuously true' is the term.) How does propositional logic treat them? How would one prove they are not contradictory?

No, they are not "contradictory", or inconsistent.

Your translations are quite a bit off, which I think only adds to your confusion. (Taking the necessary time to create an appropriate key is essential.)

Key:


Let $Px $ denote "x is a phone".

Let $Sx$ denote "x is a person"

Let $Rx$ denote "x is ringing"

Let $Axy$ denote "x is answered by y".

Using the above key:

$(1)\quad \lnot \exists x(Px \land Rx)$.

$(2)\quad \forall x ((Px \land Rx) \implies \exists y(Sy \land Axy))$.

$(3)\quad \forall x ((Px \land Rx) \implies \lnot\exists y(Sy \land Axy))$.

The statements are **not** inconsistent, since each of $(2), (3)$ must be true because by $(1)$, the antecedent in each is false.