I came across 若 from my lessons today, as in
若天下雨,我就出发。
Being familiar with 如果, I immediately assumed 若 is just a short/abbreviated/spoken form of 如果.
However, I broached the idea to my Chinese colleagues and they immediately pointed out instead that 若 in practice is a bit more stodgy version of 如果 primarily used among "elite" or pretentious types (more "formal" was their wording).
Nevertheless, this left me wondering if perhaps there's some historical truth to my initial suspicion.
若
might be a contraction of如果
? Like甭
to不用
? 若 definitely pre-dates 如果 by a big while.如果 = 如 + 果
and若 and 如 being cognates
are merely speculations on my behalf, and I don't have any references for them. That comment was merely to provide some ideas for a convincing, well-researched answer to be written.