These words refer to attempts to come between, reconcile or compromise opposing extremes. Mediate is the most general of these, carrying the most overtones of meaning. The word refers to any attempt to bring extremes together or to function as a form of communication between them: mediating between labour and management in the dispute. In this example, the implication is that the intermediary can advise or show good will but not demand or order a settlement of differences. Mediate can also be applied to the divisive disagreement itself or to its resolution: to mediate a dispute by seeking to find a middle ground on which the disputants can agree; to mediate a compromise settlement. In another use, mediate may simply indicate the occupying of a midway position between extremes: stable countries that have a sizeable middle class to mediate between the extremes of wealth and poverty. The word may also be used of something that acts solely as a link or communicating agent: a church that mediates between God and man.

Intercede stresses a coming forward to stop a dispute in progress from continuing or getting worse, although it does not necessarily suggest that such action will solve the dispute: asking the Government to intercede in the crippling transport strike. Often the word is used to suggest a third party’s being drawn into an argument in order to plead for one side or the other: asking the Queen to intercede on his behalf.

Interpose is sharply in contrast to mediate in that it suggests a blockage of communication between two hostile forces. It resembles intercede in that no solution need be applied, but the suggestion of stalemate is stronger: an international police force that could be interposed along the borders between two hostile nations. Again, like intercede , interpose may indicate entrance into a dispute on behalf of one side, although in this case the act is limited, by implication, to defence: enabling the courts to interpose themselves between an unjust law and the rights of any individual threatened by that law.

Intervene contrast with these other words by suggesting from the outset a more self-interested attitude in disrupting a dispute, usually to favour one side or another. The word would not be likely to refer to a mere stoppage, but does often suggest an intensification of hostilities: a nation refusing to intervene in the Vietnam war, though its sympathies lay with the South. As in the last example, the word can often suggest an unwanted meddling in other people’s business, and thus can impart a pejorative tone.