In the context of an ageing population and numerous challenges to wills in England and Wales, this article considers the doctrine that a testator must know and approve of the contents of his will to ensure its validity. It analyses several ostensible fundamental principles related to it, particularly in light of the potentially difficult and contradictory Court of Appeal decision in Gill v Woodall. These principles include: (1) that the propounder of a will must “prove” it; (2) that a testator with capacity who duly executes a will is nevertheless presumed to know and approve of its contents; and (3) that (notwithstanding principle (2)) “suspicious circumstances” will require affirmative proof of knowledge and approval. The article investigates the origin, normative justifications and current status of the principles, and in particular whether they are compatible with each other. It suggests a number of reforms.