Sentence:  But, for practical purposes, it is possible to draw a <WSD>distinction</WSD> between a statement of facts observed and an expression of opinion as to the inference to be drawn from these facts, and the rule telling witnesses to state facts and not express opinions is of great value in keeping their statements out of the region of argument and conjecture. 
Meaning of the word marked with <WSD> tags:  The act of distinguishing, discriminating; discrimination.