To change the subject almost completely to "weird things Plato argued", Plato recounted an interesting myth about the origin of sexes in the Symposium, that essentially humans were once male and female, with 4 arms and 4 legs and 2 faces, basically two people fused back-to-back.
If you examine human phylogeny, you will see that this isn't exactly true, but it's kinda close. Female and Male sex organs are derived from one structure in fetal development, the "gonad", which resolves into one or the other organ later during development. The full structure of male and female sex organs are actually rather visually similar (if you remove them and isolate the organ from the body, of course).
But the proto-humans or duplex-humans, not sure what its called, were too fast/strong/versatile because of these extra limbs and extra brain, Plato sort of inserting here the notion that maybe because they had 4 arms they were sort of 2x as strong/fast, these critters began scaling mount Olympus with the intention of challenging the gods, and it made Zeus a little nervous, or really i guess recognize that there would have to be a solution, even though he did not want to destroy the humans, he couldn't allow this challenge to continue.
Resultantly, Zeus decided to split the humans in two This would weaken the humans but allow them to continue most of their mortal endeavors. As a side effect, instead of vying for the power of the Olympians, they would be too rapt with lust, love, procreation to challenge the gods any longer.
Kind of cute I guess, that since they were separated in such a fashion, humans would forever yearn for wholeness that can come only from reunion with their actual other half :P
Thanks Zeus. You've really ruined a lot of my weekends.
Because they were the celestial bodies which did not move according to the general pattern.
The entire history is basically an excuse for the old "hey, we should sleep together and have fun" (shrug). Maybe it worked fine for Plato.
but it seems like he thought about it a lot :)