Thirteen for zero!! Good morning, Allison. Uncle Mark can only spare time to answer one question this morning because he must do HIS homework for Mr. University:
No, ‘be’ is not the only copular; it’s just far and away the most common. The trick here – and I mean nothing in the least crude – is to understand the word ‘copular.’ It has the same root as ‘copulate,’ meaning ‘join together.’
So, there exist intransitive verbs, such as ‘cried’ in ‘She cried,’ which take no object. There exist transitive verbs, such as ‘eat’ in ‘I ate an apple,’ which we may usefully define as ‘necessarily transitive.’ (N.b.: there are exceptions to all these: ‘She cried tears of blood,’ and ‘He lives to eat’; but let’s leave those right out of it for the second.)
However, the copular verbs, the verbs in which you are interested (which, by the way, I have heard termed ‘verbs of incomplete predication’) have A DIFFERENT NATURE -- and a good way to initially indicate this to students is to say, ‘She is . . .’ and to then make a ‘Well, come on!’ sort of gesture with your hand. The point here is that you can never use the verb ‘be’ without what I call ‘something in the box.’ Imagine that the verb ‘be’ is always followed by a box, a ‘slot.’ You can’t say, ‘She is’ because it makes no sense because she must be SOMETHING. (God, I can’t wait until someone invents italics for the Internet!!) THERE MUST BE SOMETHING IN THE BOX. That is, the subject must be joined to . . . whatever is in the box, which is traditionally (but not by linguists) termed a ‘complement.’ (Look up ‘complement.’ It means ‘that which completes.’ The crew of a ship, for example, is called ‘the complement’: no crew, ship no go nowhere.)
Is this beginning to make any sense? Now consider ‘become,’ It has a different meaning, but the same nature: you must become SOMETHING.
Now, before we go on, I suggest you do the following: explain how ‘feel’ – a copular that you didn’t list – CAN ALSO FUNCTION AS A NORMAL TRANSITIVE. When you say, ‘I felt the piece of cloth,’ you are using ‘feel’ as a normal verb. However, when you say, ‘I feel sick,’ you are using ‘feel’ as a copular.’
Hmmm . . . nearly finished now: ‘I smelt the rose’ – normal verb. ‘It smells sour’ – verb of incomplete predication. (A definition might be forming in your mind at this point: these are the only verbs THAT TAKE AN ADJECTIVE AS ‘OBJECT’ – but it’s not an object; it’s a complement – ‘that which completes’.) ‘Turn,’ I opine, is copular when you say, ‘The milk turned sour in just an hour.’ (I have never seen it on this list, but it clearly belongs.) ‘Seems’ – ‘He’s not really honest. He just SEEMS honest’ – seems (ha ha) to be ‘copular only,’
P.s.: It might help you, in the big picture, to brush up on the ‘verbs of sense’: ‘feel,’ ‘hear,’ ‘see’ et al.: ‘I heard her fall’ and ‘I saw her fall’ and ‘I felt her fall.’ They are different, but . . .