'necessity dictates' is correct and usable in written English.
It is used to indicate that something is necessary and therefore should happen. For example, "Necessity dictates that we take action quickly to protect the environment."
Economic necessity dictates that Saudi Arabia reforms now".
Necessity dictates what must be done for the body before anything can be done for the mind.
Abortion is the fourth wheel beneath the Republican values bus, to be rhetorically inflated or deflated as political necessity dictates.
Indigenous people in Latin America face all kinds of discrimination, and necessity dictates that, sooner or later, they adopt Spanish.
Stone acknowledged the situation the White Sox face with the health of Jake Peavy seemingly an inning-by-inning proposition, admitting "necessity dictates what you do".
Yet we need to do it in a way that preserves our flexibility to act with or against regimes as necessity dictates, particularly since friends and enemies may change places overnight.
Therefore, necessity dictated that Mozambique's military be larger than those of surrounding countries without such internal strife.
Necessity dictated that we spent as much time together as we could, and there was no better, more acceptable time to do that than the fag break.
But poor parents are slightly more likely to let their children go to the store alone, a case of necessity dictating behavior.
Of more pressing concern is the small matter of the Irish domestic football season played through the summer these days, with fiscal necessity dictating that the contracts of Rovers' players expire in November.
It is not, as Boehner would have it, a policy necessity dictated by the inability of the federal government to borrow or tax sustainably.
