I have gone through several threads here but haven't found an answer to my question.
In my paper, there are two theorists and each has a theory. Theorist A has theory 1 and theorist B has theory 2.
Can I use both example 1 and example 2 and express this fact?
1) A's and B's theory are worthwhile considering. 2) A's and B's theories are worthwhile considering.
I reckon that 1) is a form of ellipsis standing for A's (theory) and B's theory... Does 2) imply that both A and B have EACH devised more than one theory or that I include A's theory and B's theory to form the plural "theories"?
And on a similar note, Bohr has written one book on a subject and Gitman has written one book:
3) The Bohr and the Gitman volume are worthwhile considering. 4) The Bohr and the Gitman volumes are worthwhile considering.
Which one is correct?