Certainty and uncertainty

Apprehensive

Anxious or fearful about the future; uneasy

Categorical

A. Without exception or qualification; positive; absolute
B. Of or in a category.

Conclusive

Serving to put an end to doubt, question, or uncertainty; decisive; convincing.

Dubious

A. Doubtful; uncertain.
B. Questionable as to quality or validity

Indeterminate

A. Not capable of being determinated or decided; not precisely known; indefinite.
B. Lacking clarityor pcision; vague; indeterminate data

Inevitable

Incapable of being avoided or prevented.

Precarious

Dangerously lacking in security or stability; unsafe; risky.

Qualm

A. A sensation of doubt or misgiving; uneasiness.
B. A pang of conscience.
C. A sudden, brief feeling of sickness, faintness, or nausea

Unequivocal

Leaving no doubt or misunderstanding; perfectly clear.

Vacillate

To waver indecisively between one course of action or opinion and another; hesitate.