Yes, I'm sorry. I wasn't intending to be dismissive, but I see that the comparisons I picked could seem that way. It was what I saw as a marginal difference between the two expressions that I was trying to articulate. But I did think that either could be used, in the right context, to describe either a reciprocal or a wandering activity with back and forth slightly weighted towards reciprocal.

I wrote some more to develop that theme and the more I wrote the less certain I became of what I thought. In the end I looked into the Concise Oxford and it said: “to and fro = backwards and forwards, repeatedly, between the same places”; “back and forth = to and fro”. So I deleted what I had written and concluded that I know nothing. A conclusion I reach with greater frequency from year to year!

In cricket, the batsmen run between the wickets. They could be said to run to and fro, back and forth or even up and down! I drive to work each day; I could be said to drive to and fro or back and forth. I use several quite different routes and rat-runs however so, unlike the batsmen, there is irregularity within the regular activity – to some extent I wander. Neither of these expressions, it seems, clearly gives that difference without some context.