quality an essential and distinguishing attribute of something or someone; "the quality of mercy is not strained"--Shakespeare
doubt,
doubtfulness,
dubiousness,
question uncertainty about the truth or factuality or existence of something; "the dubiousness of his claim"; "there is no question about the validity of the enterprise"
improbability,
improbableness the quality of being improbable; "impossibility should never be confused with improbability"; "the improbability of such rare coincidences"
fortuitousness the quality of happening accidentally and by lucky chance
Uncertainty -
the state of being unsure of something
indecision,
indecisiveness,
irresolution doubt concerning two or more possible alternatives or courses of action; "his indecision was only momentary but the opportunity was lost"
peradventure doubt or uncertainty as to whether something is the case; "this proves beyond peradventure that he is innocent"