Use the subjunctive mood in that-clauses thatare the complements of verbs expressing an obligation or a demand (for instance,advise, ask, command, demand, desire, insist, propose, recommend,request, or suggest) and to express conditions contrary to fact.
The consultant recommended that the staff be recertifiedin laboratory safety procedures.[that-clause expressingobligation or demand]
If the Earth were the size of a basketball, its surfacewould be smoother than a basketball's. [condition contrary to fact]
Do not use the auxiliary do when you negatethe that-clause with not.
When you are performing this procedure, it is crucial that the temperaturedoes not rise significantly.
When you are performing this procedure, it is crucial that the temperaturenot rise significantly.
The conditional, often considered a variety of the subjunctive, is used toexpress states or actions contrary to fact, but whose truth or possibleimplications you would like to consider. In particular, use the conditional inif clauses whose conditions are not true. To form the conditional for the present tense or thefuture tense, use the pasttense form of the verb.
Researchers assume that a nuclear war would raise anenormous pall of thick, sooty smoke from massive fires that wouldburn for days, even weeks, following an attack.
--C. Donald Ahrens, Meteorology Today
If we could travel far beyond the protective blanket ofair that shelters our planet, beyond the ancient craters of the moon, and beyondthe orbits of the nine known planets, we would reach the realmof interstellar space, where our solar system leaves off and the rest of theuniverse begins.
--Andrew Fraknoi, "The Universe: An Introduction"
To express the past tense of the conditional, add the auxiliary haveto your verb phrase.
Scientists should have recognized the possibility ofblack holes in 1916, when the German astronomer Karl Schwarzchild succeeded insolving Einstein's equations for the gravity surrounding a point mass.[The combination of should (conditional) and have (past)signals that this was an unreal past action; the recognizing did nottake place.]
--William J. Kaufmann, "The Black Hole"
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