Let us take the senate (100 persons). Simple majority to pass. (51%) It everyone votes, it takes 51 votes to pass something. Let's say 10 reps don't vote. So long as 51 votes are still demanded, they are being counted as 'No' votes by default. Sine they refuse to go on record on vote, shouldn't it be 51% of votes (in this scenario, 51% of 90 = 46)?