Frequently, catch phrases are not, in the grammarians’ sense, phrases at all, but sentences. Catch phrases, like the closely linked proverbial sayings, are self-contained, as, obviously, clichés are too. Catch phrases are usually more pointed and ‘human’ than clichés, although the former sometimes arise from, and often they generate, the latter. Occasionally, catch phrases stem from too famous quotations. Catch phrases often supply—indeed they are—conversational gambits; often, too, they add a pithy, perhaps earthy, comment. Apart from the unavoidable ‘he-she’ and ‘we-you-they’ conveniences, they are immutable. You will have perceived that the categories Catch Phrase, Proverbial Saying, Famous Quotations, Cliché, may coexist:they are not snobbishly exclusive, any one of any other. All depends on the context, the nuance, the tone.