Are conventions arbitrary?

Well, yes (to the title question).

I chose that title for its brevity.  This post is intended to explain what it means to say that conventions are arbitrary.  But that’s a bit long for a title.

We generally adopt conventions for a reason.  For example, the convention that we drive on the right side of the road was adopted to reduce the likelihood of head-on collisions.  But it would work just as well to drive on the left side of the road (as they do in Britain and Australia).  So there was a choice to be made between the two.  That particular choice was an arbitrary choice — it would not matter which way you chose, at least with respect for the reason that the convention was adopted.

There are all sorts of other options that could have been chosen.  It could have been decided to drive on the right for one mile, then on the left for the next mile.  Or it could have been decided to drive on the right on Monday, Wednesday and Friday, and on the left on the other days.  But these kinds of choices would have been confusing and would therefore have been less effective in reducing head-on collisions.  Pragmatically speaking, it boiled down to only the two choices — left or right.

The use of the word “arbitrary” seems confusing at first, because it seems to suggest “random”.  But conventions are not random.  What we mean, when we say that they are arbitrary, is just that they are not fully determined by reality.  Adopting a convention usually means some kind of choice.  But, although not fully determined by reality, that choice is still guided by the goals that have led us to adopting a convention.