Language emanates from intelligence. That means the patterns and structure that make up human intelligence will appear in language. LLMs are created through so much language training that they can approximate (and now to some degree exceed) human intelligence using pattern recognition, statistics, and autocomplete (in layman’s terms).

Not sure how it is now, but early “reasoning” was simply the big labs sticking “wait a minute, what if I…” type language blocks into the process to trigger something like our own internal reasoning.