The Wikipedia Watchword of the Day--2/23

The Wikipedia Watchword of the Day is

Reductio ad absurdum

A trickier, but even stronger reduction from the philosophical point of view, because it does not rely on A's accepting that D's opinion is wrong, would be the following.

A — You should respect C's belief, for all beliefs are of equal validity and cannot be denied.
B —

1. I deny that belief of yours and believe it to be invalid.

2. According to your statement, this belief of mine (1) is valid, like all other beliefs.

3. However, your statement also contradicts and invalidates mine, being the exact opposite of it.

4. The conclusions of 2 and 3 are incompatible and contradictory, so your statement is logically absurd.