The following contexts allow expletive the complement clause of verbs expressing fear or avoidance: (to fear), (to be afraid), (to prevent), (to avoid) the complement clause of verbs expressing doubt or denial: (to doubt), (to deny) adverbial clauses introduced by the following expressions: (before), (unless), (for fear that) comparative constructions expressing inequality: (other), (better), (stronger), (less intelligent), etc.
The following contexts allow expletive the complement clause of verbs expressing fear or avoidance: (to fear), (to be afraid), (to prevent), (to avoid) the complement clause of verbs expressing doubt or denial: (to doubt), (to deny) adverbial clauses introduced by the following expressions: (before) (unless), (for fear that) comparative constructions expressing inequality: (other), (better), (stronger), (less intelligent) etc