prepositions - difference between 'beneath' and 'under'

And finally (since he had started looking at the inadequacies of his life, why not make a comprehensive survey?) there was his recent weight gain; a full stone and a half, so that he not only felt fat and unfit, but was putting unnecessary additional strain on the prosthetic lower leg he was now resting on the brass bar beneath the table....... He returned to the bar to buy a third pint. Back at his table beneath the cupola, he drew out his mobile phone and called a friend in the Metropolitan Police whose friendship, though of only a few years’ duration, had been forged under exceptional conditions. (The Cuckoo’s Calling, by Robert Galbraith)

The chart that a grammar text has drawn says that ‘beneath’ is under a position, making contact with underneath of something; and ‘under’ is lower than that. But it seems not like that way when I look up Merriam-Webster’s examples below and the above example from Galbraith's story book. I rather say that 'under' and 'beneath' are used with the same meaning.

We had a picnic beneath a large tree.
We sat under a tree and rested a while.

the ground beneath [=underneath] her feet
I'm wearing a sweater under my jacket.

Does the chart deliver wrong message or was it making sense in the past - the text was written in 1967 ?

Answer

As far as the chart you reproduce is concerned I think it's misleading, there's no difference in position between beneath and under and both should be on the same level.

I would say that beneath and under are near synonyms, they both mean that something is lower than something else. The essential difference is in register. Beneath is more formal, more literary. The choice of one over the other depends on what you want to convey.

I'm wearing a sweater under my jacket.
I'm wearing a sweater beneath my jacket.

both mean that the jacket is on top of the sweater.

Some people might see a difference between:

(1) The ground under my feet.
(2) The ground beneath my feet.

1) referring to the actual piece of ground my feet are touching
2) referring to the ground in general, or a larger piece of ground than just the actual piece my feet are in contact with.
I would say it is context dependent and I would use beneath in both cases, and maybe not under if I meant the ground in general.

When used in an abstract way beneath is preferred to under.

• Myrtle Wilson (in the Great Gatsby), married beneath her class.


• If I find that something is beneath my dignity, it means I have such a high opinion of myself hat I could not do it without degrading myself.

But:

We have a lot of work at the moment and we are under great stress.

Note:

As in you examples I have only considered the use of both words as prepositions. But note that under is very rarely used as an adverb (I can't think of an example where it would be used as one - which does not mean it is impossible, of course) whereas underneath can.

The garden is just under/beneath my bedroom window. (preposition - it is followed by a noun)
When I look out of my window I can see the garden beneath/underneath. (adverb)