These words are concerned with the development of plans for solving a particular problem. Devise and contrive both stress the actual working out of the plan, detail by detail. Devise is neutral in tone, making no comment on the value of the plan or its objective; it also emphasizes the tentative nature of the proceedings, suggesting that many possibilities are entertained, used, rejected or revised: devising proposals to deal with air pollution; devising a strategy that could win the battle. Contrive is similar in most respects to devise except for its tone which may now suggest a conspiratorial or illicit plotting towards unworthy ends: contriving a fool-proof scheme for robbing the bank. In a different but also negative sense contrive may suggest unrealistic planning, needless complication or artificial devices that avoid the problem rather than solve it: a law so contrived that the average person could not possibly understand or obey it.

Conceive refers to a point in the planning process that must precede devising or contriving . The word suggests the first ideas that form themselves in a person’s mind when faced with a problem, but before these ideas have necessarily been tested by the process implied in devise . He devise an escape from it. Formulate , by contrast, refers to an act that follows devising , in which the rough plan is spelt out, formalized, or put into words. Each step of the whole planning process may be evaluated separately.

• The proposed law, while brilliantly conceived , has been poorly devised to do the job at hand; even worse, it is so vaguely formulated that it invites misinterpretation.

Invent is a word much larger in scope than the others here. It includes the whole planning process ?conceiving , devising and formulating . Also, its product is more often an actual object than simply a set of procedural techniques: inventing new synthetic fibres; inventing new techniques for coping with juvenile delinquency.