Absurd means opposed to reason or truth, and may be applied to that which is grossly, and sometimes grotesquely, inconsistent with common sense or experience. Preposterous denotes a great contrariness to nature, reason, or common sense, and is used to describe that which is outrageously absurd . Ridiculous refers to that which is absurd in a way that invites ridicule or mockery.

• It is absurd to predict that the sun will not rise tomorrow; it is preposterous that virtue should go unrewarded while vice goes unpunished; It is ridiculous to judge a foreign culture by its plumbing.

Farcical and ludicrous are applied to that which is absurd in an amusing way. Farcical indicates a humorous distortion of fact, convention or reason. Ludicrous implies playful absurdity , but may also be synonymous with ridiculous in describing something that is greeted with scorn or derision.

• The farcical introduction of a talking horse gave the play its flavour; The ludicrous antics of the harlequins delighted the audience; The speaker made a series of ludicrous mistakes which were rewarded with hoots and catcalls.

Foolish , senseless and silly add a suggestion of folly or even of a trivial intellect to their synonymity with absurd .

• To buy shares in an unlisted wild-cat enterprise is a foolish investment; To beat a dead horse is senseless ; To make unsupportable claims is silly affectation.

Unreasonable and irrational mean contrary to reason, the difference between them being the fact that unreasonable implies a bias or intent to go wrong and irrational suggests an uncontrollable lack of understanding.

• It is unreasonable to maintain a geocentric theory of the universe; It is irrational to expect an adult reaction from a child.