Like I said, I'm not trying to dictate the vocab, I'm just letting you know. As long as I know what you mean and you know what I mean, there's no problem.
But what is heat? What is fire? In what manner does fire "produce" heat? These were philosophical, even religious, questions until modern science came along, with myriad guesses, opinions, and dogmas. I mean look at the sun, which you brought up. People might have opined that the sun produced heat, but they simultaneously looked on it as a deity. They might have consequently opined that if the sun produces heat, the moon produces cold. Or, that light and heat have no relation, since the moon clearly produces light just like the sun, but the night isn't warm like the day. There was no rigor, just inference from very vague, very unempirical evidence, and definitely no real understanding of the dynamics at work. So they might have had some knowledge, but no context, no systematic, connected view of the world in which to arrange these little snippets of what I would consider mostly coincidental knowledge.
Well, you seem to be criticizing them for not having it all together. It is plausible 1000 years from now, this date and time will be scoffed at and ridiculed for not having it all together. However, failing to have any understanding of the dynamics at work, or a unifying theory of the world in which these phenomenon exist, does not diminish their knowledge fire/sun produces heat and light. The fact they did not espouse a more complete theory of heat and light, such as light is waves and particles, invisible entities called atoms, and when the electron gets excited, it produces what your eyes detect as light, does not diminish the knowledge they possessed from their mental recognition of a connection between fire/sun producing heat and light.
Those primitive screwheads probably did not know anything about sperm, egg, dna, fertilization, and so forth. Yet, this does not diminish the knowledge they possessed by observing doing X with cavewoman Y results in the birth of a human being. Yeah, they failed to understand the intricacies of why this is the case, sperm, sperm, eggs, ovulation, falloppian tubes, but this failure does not diminish the knowledge they had, no matter how primitive, that sexual intercourse produces a child.
Now, this is knowledge which allowed them to survive, knowledge they used to facilitate their survival. This is knowledge they conducted and conformed their behaviors around. It was an unchanging knowledge as at no time did they observe fire not produce light or heat. They conformed their behavior around it, being in a better position to survive in a harsher environment, realizing they could make fire and the heat/light from the fire assisting them to better survive the tough environment.
In the book, "Moral Animal," by Wright, an advocate of evolutionary psychology, the idea is primitive man made some rather knowledgeable deductions, although simplistic by today's standards, but nevertheless knowledge, and still with us today.
For example, in general the male's attraction to younger women, young women in general, is the result of primitive man, and afterwards, using this as a standard for determining whether the woman could have a child or not. The idea being primitive man came to the realization, knowledge, some women, older women, did not produce a child after having sex with them, whereas younger women did. Now to be sure, they did not have any knoweldge of how the female body stopped producing eggs at some point, but it just so happens their standard coincided with this phenomenon. This is why men today leave their 40 plus year old wrinkled old wife for a younger, more vibrant sex kitty, because primitive man used this physical appearance, this physical distinction, as a predicate of who they would have sex with.
They of course used this understanding of what they sensed, what they perceived, and the deduction they made from it, to ensure their survival, by of course sleeping with the younger women, thereby producing human beings, and perpetuating the species. In other words, they used this knowledge to ensure the survival of the human race, and it worked, much like it would work today, and our knowledge works for us today.
The point, however, is they had knowledge old women did not reproduce. They may have not known why but they made the mental connection they could not. Now this is knowledge, regardless of the fact they failed to espouse a theory of explanation stating the aged women had no eggs to fertilize.
My point here, once again, is this is knowledge, and it is knowledge which has not changed in thousands of years. I think the constant here is compelling evidence we are not in some dream, what we perceive as reality is not fake or phony, and neither a machination of our minds.