the.com/positive

means Certain beyond doubt, or — in the other sense — constructive and affirmative rather than negative.

from From Latin positivus, 'settled by agreement or position,' from ponere, 'to place or put.' Originally it described laws or rules 'laid down' by authority rather than derived from nature — hence 'positive law.' The sense of psychological certainty ('I'm positive') grew from that same idea of something firmly 'put in place,' no longer up for argument — which is exactly the mood right before the argument restarts.