The complex sentence with an adverbial clause of purpose 853
§ 173. Clauses of purpose generally express the purpose of the action, which is stated in the main clause. The verb-predicate in the subordinate clause is in the subjunctive mood as it expresses a planned but not a real action. Adverbial clauses of purpose are introduced by conjunctions that, so that, lest, so as, so, in order that, for fear that.
I trode on an edging of turf that the crackle of the pebbly gravel might not betray me.
I tell you all this so that you may understand me perfectly.
The conjunctions lest and for fear (that) introduce clauses stating what is to be prevented, as botli the conjunctions have a negative meaning. Lest is now extremely formal and after this conjunction the analytical subjunctive with should auxiliary is generally used.
He was like a man who is afraid to look behind him lest he should see something there which ought not to
“It’s a bit lighter in the park,” he said, “but take it (an electric torch) for fear you get off the path.”
In some cases the meaning of purpose in clauses introduced by lest and for fear that is weakened so that the clause expresses rather general motivation than purpose,or else an outcome of the action in the main clause, as in:
Lest the wall should collapse, they evacuated the building. (They did not evacuate the building with the
purpose of causing the wall to collapse.)
Better chain up the dog for fear he bites.
The conjunctions that, so that, lest, so are not confined only to clauses of purpose: that may introduce subject clauses, predicative clauses, and object clauses;
so that may introduce clauses of result, lest - clauses of cause, subject clauses, predicative clauses and object clauses; so - clauses of result and of cause.