invoke

Close kin to calling something to mind, but here what is called on must carry weight, such as a scripture, a constitution or a great name. In some circles, invoking the Bible settles an argument outright. Philip Ziegler's The Black Death (1969) shows the scholarly use: a writer invokes cadaveric poisoning as a cause, putting an explanation forward and standing behind it.

The oldest picture in the word is a raised voice. Latin invocāre, "to call upon," is built from in- and vocare, "to call," and reached English through Old French envoquer. The object is the one addressed, such as a saint, a god or a patron. What is sought follows as protection or aid. Invocate is the same Latin word borrowed a second time and is now obsolete. It is a doublet, not a variant spelling.

The workhorse of argument: a writer invokes a law, a principle or an idea in order to put it to work. John Stuart Mill writes that a wife "could invoke no law against him," and Darwin asks whether "any new principle has to be invoked." The word is easily confused with evoke, and purpose is the difference: something invoked is brought to mind in order to be used.

Here the call goes to a quality rather than a person: an envoy invokes a king's magnanimity, not the king himself. The object is the disposition hoped for, such as goodwill, mercy or compassion, and that is what separates it from calling on a god for help. Modern Railways in 1964 writes of pressures that "invoked the Minister's diktat," where pleading shades into producing.

The ritual sense, where calling becomes summoning: the words of the rite are meant to make the spirit appear, as when a ritual invokes Beelzebub. It differs from asking a god for help in what the speaker expects, which is the being itself rather than aid from a listening power. Summon is the near synonym, but invoke keeps the sense that the words do the work.

Programmers use invoke and call almost interchangeably, but invoke is the wider word. Stephen Prata's C++ Primer Plus (2011) explains that an operator function can be invoked either by calling it or by writing the overloaded operator in its usual syntax. In the second case it runs without any visible call in the code. Computerworld was already speaking of "invoking time" in 1974.

Seafaring keeps the root meaning closest to the surface. One ship calls another, by hail or by signal, to make contact, exchange information or ask for help. Both subject and object are vessels: the crew does the work, but the ship is said to invoke. Signal is its nearest plain-English equivalent.