Assumption, deduction (9)
I believe the answer is:
inference
I believe this clue is a double definition.
'assumption' is the first definition.
(thesaurus)
'deduction' is the second definition.
(I've seen this before)
(Other definitions for inference that I've seen before include "Conclusion reached on the basis of evidence and reasoning" , "Niece fern (anag.)" , "Deduction, conclusion" , "Deduction from evidence" .)