The verb will in English is probably one of the most amazing in the entire language in my opinion, not just because I will it to be that way. It has absolutely so many uses and derivations within English.
For example, it can be used to express want. In the sentence above, I said ‘I will it to be that way’ where I could easily have said ‘I want it to be that way.’ Yet in this example, will seems out of place to a native English ear and seems archaic or quite rude. In English, there is a strange dichotomy between will and want, which have similar meanings, but very different usages.
It wasn’t always this way. In Old English, the verb willan (will) was used where we would use want. For example, here’s a sentence from the medieval romance Apollonios of Tyre.
Forðam gif hit gewurðan maeg, ic wille me bedihlian on eowrum eðle.
And so if it may come about, I want to hide myself in your country.
So then, this begs the question of when want came on the scene. It comes from the Old English verb wanian (lessen, diminish, wane) which had the original sense to lack and be in want of. Later it came to be used in the place of will. I would like to suggest that willan and wanian come from the same root in Proto-Indo-European meaning ‘to lack’ or ‘to be in want of.’ Similarly we might attribute the case of the verb wish which comes from Old English wiscan. This is no more than will plus the verb suffix –sc which acts as an intensifier signifying repeated action (cf. Latin –sco and Greek –σκω). When you wish for something, you want it multiple times after all.
And so, to return to our discussion of will and want, when did this distinction between the two arise? Probably, most likely when the verb will started to be used to express the future, the difference arose as people looked for a way to avoid confusion. And so the verb want mostly replaced will when it came to expressing volition.