Questionable
Part of speech: adjective
Definition: Problematic; open to doubt or challenge Of dubious respectability or morality
Example sentence: The tendency of modern scientific teaching is to neglect the great books, to lay far too much stress upon relatively unimportant modern work, and to present masses of detail of doubtful truth and questionable weight in such a way as to obscure principles.
Refutable
Part of speech: adjective
Definition: Able to be refuted, or shown to be false.