Quote Originally Posted by Maciamo
If 論拠 means "grounds for an argument" (which for me isn't the same as simply "argument"),
It just happens that in English 'grounds for an argument' means the same as one of the meanings of 'argument' in English.

how would we say then : "The grounds for your second argument are not valid" ? The grounds is 論拠, but what becomes of the "second argument" part ? Still no translation I guess.
But 二つ目の論拠 IS "The second grounds for your (argument/position)".