A repugnant act cannot be brought into being, i.e., cannot be made effectual.

Explanation

(English-origin maxim.) An act that contradicts itself or is internally inconsistent is void — the law will not give effect to what is self-defeating.

Where this applies

• A deed grants land to someone 'and his heirs forever' but then says the grantee can never sell or transfer it — the two clauses contradict each other, making the restriction void.
• A contract says the seller will deliver goods 'at buyer's discretion' but also requires delivery by a fixed date regardless of buyer's request — the self-contradicting terms cancel each other out.
• A will leaves the entire estate to one daughter but a later clause in the same will leaves the entire estate to a different daughter — the repugnant provisions cannot both stand.