Why is it 'in the saddle' rather than 'on the saddle'?

Question

I regularly hear the phrase 'in the saddle' but 'on the saddle' seems more appropriate as you are literally on top of it, (I'm using the original definition of literally there!).

I can sit in an armchair. A baby can sit in a high chair. I can sit in a car.

Up to this point, it seems that if the object you are sat in/on surrounds you in some way, then you must sit in it.

I can sit on a plane (at least I've never heard someone say "I'm sitting in a plane right now"!), which is weird because you're actually inside the plane!

But i can only sit on a sofa, no one ever sits in a sofa.

So what gives? Is it just the fact that one option sounds better than the other, or is there some deeper understanding of the English language that I am missing?

Answer 1

Both "in the saddle" and "on the saddle" are used. The difference lies in what you want to say. "On the saddle" is merely a description of the position, while "in the saddle" means "in control". I guess you could imagine an emperor sitting in his giant chair, compared with a commoner sitting on his/her little chair, for an analogy.

The same goes for "in the bed" and "on the bed". "On the bed" is a description of position, while "in the bed" implies in addition being covered by something (a sheet for example).