Absolute Signal Words
These words should make the reader reject a statement unless there is strong support.
always, definitely, irrefutably, assuredly, indisputably, undeniably, certainly, invariably, without question, etc.
Probability Signal Words
These words suggest that the information may be accurate but that other possibilities may exist.
almost, probably, presumably, there is little question, etc.
Possibility Signal Words
These words suggest that the ideas are subject to debate and that there is doubt as to their complete validity.
apparently, may/maybe, possible, somewhat, could be, might, seems, likely, perhaps, seemingly, etc.