An argument from an impossible consequence to an impossible antecedent is valid only where the necessary relation is established under the same conditions. An impossibility arising after adding an external condition needs not be an impossibility in the act’s essence.
“Zayd believes” is intelligible as an action. “Zayd believes and an infallible report of his nonbelief remains true” is a different, compound claim.
The impossibility of a conjunction does not establish that every component is intrinsically impossible. Logical qualifications matter.