Humans began to rapidly accumulate technological knowledge 600k years ago

I'm highly suspicious that the whole "inner vs no-inner monologue" thing doesn't actually exist and has more to do with these things being extremely hard to explain using language, and people describing their subjective experience in subtly different ways.

I 100% do not think in words or sentences or language. It feels more like node-traversing a graph of concepts, but it's all completely abstract. While I am able to consciously play back my thoughts linguistically or visually with some effort (and at the cost of efficiency), by default there are neither words nor images.

French is my first language, I'm fluent in English, and I know a bit about many languages... But I've never had an inner voice or thought in language, even when I was very young.

Right, very like me. Language is the front end; I use it to express thoughts when needed (to record, communicate and check reasoning) The back end is working in some kind of abstract space.

I suspect people who say they think in language are not really thinking "in" language. I think we all have this abstract conceptual space in us. I'm not even sure what it means to think in language; where do the ideas and concepts come from that are being expressed? I guess some people have to internally "hear" a thought expressed before it is real to them.

What I am saying is that probably everyone thinks the way you do, it's just that not everyone would describe it in that way. For example, I'm sure you came up with this comment in your head at some point before typing it and many people would describe this as an inner monologue, whereas you apparently do not.

Good, I have the same suspicions about "no mental imagery vs. vivid mental imagery". Perhaps people who claim either thing are just being, uh, imaginative.

Yep, make a statement like this and somebody will always pop up and say "but me, but I, because I characterize my inner experience as such-and-such and I like to think of myself as special ... that makes the distinction real."

Internal monologue (or dialogue, as it can play out as imagined conversations) is an apt name for it. Imagine reading a play. Everything is expressed as language, and ideas and concepts are expressed through that language.

Oh, perhaps. And I didn't mean to suggest that I was special in any way, but... When I discuss this with people in real life, it is very rare that I find someone who relates to this way of describing how I think. Most people are just stuck in literal wide-eyed disbelief and either tell me they think in literal words, fragments or sentences, experiencing a real "inner voice", or they tell me that they visualize things somehow.

Sometimes people seem to not be sure how to describe the experience of thinking... Which I suppose explains a lot! /laughs