Reason, ground, argument, proof are comparable when they mean a point or series of points offered or capable of being offered in support of something questioned or disputed.
Reason usually implies the need of justification, either to oneself or another, of some practice, action, opinion, or belief; it is usually personal in its reference; thus, a father asks the reason for his son’s disobedience; a person gives the reasons for his preference. Reason is often applied to a motive, consideration, or inducement which one offers in explanation or defense.
Ground is often used in place of reason because it too implies the intent to justify or defend. When, however, the emphasis is on evidence, data, facts, or logical reasoning rather than on motives or considerations, ground is the acceptable word; thus, the reasons for a belief may explain why it is held, but the grounds for it give evidence of the validity of that belief; a scientist presents the grounds for his conclusion.
Ground also suggests more solid support in fact and therefore greater cogency and objectivity than reason; thus, one may speak of frivolous or of trumped-up reasons but not grounds .
Argument stresses the intent to convince another or to bring him into agreement with one’s view or position. It can imply the use of evidence and reasoning in the making and stating of a point in support of one’s contention, but often it suggests reasoning without reference to fact .
Proof in much of its use (see proof under PROVE ) emphasizes not an intent but an effect: that of conclusive demonstration; therefore, a proof is a piece of evidence (as a fact or a document) or of testimony (as of a witness or expert) or an argument that evokes a feeling of certainty in those who are to be convinced.