This is a wonderful (in an infernal way) term popularized by Al Gore. Since he is a rascal, he was doing illegal fundraising, collecting wads of cash from foreigners. When it all hit the fan, one thing he said in private that became public was that he would proceed with these illegal activities because they had "plausible deniability." That is, he knows he did it, and everyone else does too, but he has an excuse that, while not convincing, cannot be disproved. Hope you could follow that.

Now, Al is not alone in this and we all stoop to it sometimes. You're in the kitchen to steal cookies and when you're caught there you explain that you were there to do the dishes. Everyone knows that's a lie, but it can't be proven as a lie, so it's hard to punish you. And if you DO get punished, you get to bitterly protest your wounded innocence the whole time. Man, you were just trying to HELP AROUND THE HOUSE and look what you get from those fascists, etc.

In fact, plausible deniability is fantastically useful, as just a moment's reflection will show. People can and do use it all the time to be contemptible scoundrels and get away with it. Two problems. Maybe more than two. I'll know when I stop typing.

First: since nobody is fooled, people are quite aware that you are acting like a scoundrel. The more you do it the more you benefit by getting away with stuff, but the more you suffer in lost trust and esteem. And the payback from that one is really bitter. People you need are going to just give up and walk away.

Second, and worse: just because of the way our minds work, if you loudly insist on something that is not true, you will begin at some level to believe your own lie. If you do it a lot it can actually detach you from reality. Not only can you badly damage your ability to see the truth, but you can actually lose your ability to tell the truth. You can reach a point, like Al Gore, where you are the only person who does not realize you are a scoundrel. Using plausible deniability destroys your character, and it can do it pretty fast.

I had a boss for a number of years so I got to watch him closely. I realized that he was an habitual liar. I eventually realized that he lied even if it didn't matter- he would lie about completely harmless things. It was as though looking at reality, observing it, and then reporting what he saw was just too inconvenient. It was easier and more customary to just make something up, and say it. He lied continually, about absolutely everything, and would protest loudly and bitterly if he was not believed. I think he no longer realized he was not telling the truth. And I think the term for that is "pathological liar."

So in a very profound sense, this man had been morally destroyed. And he didn't even know it! That will never happen to you and me, huh? Well, it's a long process of small steps and each step is harder to prevent if you've taken the previous step.

Lesson? Don't use plausible deniability. Say what you really did, and really why you did it, or don't say anything. In particular, when you are in conflict with someone, you tend to be looking for any kind of defense. At such times, plausibility seems more valuable than truth. "I said it because I care" is much more strategic than "I said it because I was trying to hurt you." But don't destroy your character that way. Just don't start.