Hi all.

My best friend and I are both super opinionated on various topics will get into debates fairly often. All kinds of topics. Religion, alien life, morals, etc. In the past few years I've avoided contentious conversation with him because when he starts feeling like he's wrong or can't refute my points in a reasonable way he uses this debate tactic that I think is super disingenuous and frustrating.

The easiest way for me to explain what he's doing is an example. For the sake of brevity below is just a summary. I cut out most of it as the actual debate doesn't seem super important to label the tactic. There was a lot more in the beginning and I've totally skipped to the end. The important part i'm trying to show is the end.

Friend: I don't think there is alien life in the universe.
Me: Ok, why not?
Friend: We now know that there are tons of planets in the Goldilocks zone and we haven't seen any incoming signals.
Me: I don't see how you get from lots of planets in the Goldilocks zone and no detectable signals to no alien life. What if life is just extremely far apart and the signals haven't reached us or we don't have the knowledge or tools to detect them.
Friend: It's odd. We should have gotten signals by now.
Me: I'm not convinced it's odd. Since earth is the only planet known to have life how can you say it's odd if you don't have anything to compare it against.
Friend: All scientists think it's odd, it's odd.
Me: How do you define odd? I would be okay if you said it was interesting instead of odd.

Friend: Words don't even have meaning.
Me: What are you talking about? Of course words have meaning.
Friend: Only the meaning we give them. You can define them however you want. Have you ever read a white paper? You can define words however you want in the beginning.
Me: You can't define words however you want and you definitely can't redefine colloquial terms totally differently.
Friend: Yes you can. Why not?
Me: So I write a paper tonight claiming the sky is red. I define red as blue in my paper. Do you think that's honest and I can do that?
Friend: Yes.
Me: I'm done with this conversation. When you're at the point where you say words don't have meaning I don't see how I can argue with you.

So that's an example but that happens all the time. I think when he feels backed in a corner and doesn't have any way to refute my points he suddenly opens an escape hatch by reverting to a philosophical argument about the meaning of words and how they can mean whatever he wants. The most annoying thing is when I don't realize he's started down that road and terms we've been using for the whole conversation start changing without me realizing it.

Sorry for the long post. After every argument I try to explain why I think what he's doing is disingenuous and wrong. I'd like to see if I can track down some info if there is a name in debate for this tactic. I've seen a few close but none seem an exact match.