can we say sentences like "used to be able to be..."

Question

What is the problem with this sentence, grammatically: I used to be able to be flexible.

I think the part "be flexible" isn't true grammatically because of the second "be". I don't know; it seems a little bit odd.

Answer 1

The problem that some people may have with your example sentence is that you mix up an action and a state.

Sentences like

The book is green.

or

I am flexible.

describe what something is, a state. In contrast, sentences like

The book falls down.

or

They cook dinner.

describe what something or somebody does, an action.

With "to be able to", you typically use an action:

I'm able to read a book in French.
He's able to calm down the snarling dog.

But your example sentence combines "to be able to" with a state, "to be flexible". So while it's not technically wrong, some might consider it unnatural. Something like

I used to be able to flex.

or

I used to be (more) flexible.

would be more natural.

So in general, "I used to be able to do something" sentences are just fine, but combining "to be able to" with a state instead of an action might trip some people up.

Answer 2

Repetition of 'be' in your example sentence is neither incorrect nor ungrammatical. Some people may find the repetition to be inelegant or clumsy, and may prefer something like 'Previously I could be more flexible', that is, finding a substitute for 'used to be able to'.

Answer 3

There is no grammar mistake. The sentence is a little clumsy, but I think the reason for this is the meaning of "flexible", which is (literally) "able to flex".

So your sentence says "I used to be able to be able to flex." Using "be able to" with adjectives that end in -able (or -ible) is often not necessary. Here you could say "I used to be more flexible". This is related to the meaning of "flexible" and not to any grammar rule.

Similarly you would not often say "She's able to be flexible", unless you meant "she isn't flexible now, but if she chooses she can become flexible."