is ing form possible with modal verbs?

[Sonia*]

A very sweet good morning to all and sundry ESL Teachers.

I read in a grammar books in my school days that "The modals can,could.may,might,shall,should,will,would,must and ought are termed Defective Verbs,because some parts are wanting in them.They have no -s in the third person singular:they have no infinitive and "ing" forms.

but after this I read so many sentences which have ing form with modals like in the following sentence;
1) "I could not be leading a religious life unless I identified myself with the whole mankind and that I could not do unless I took part in politics".
2)she must be calling you.
3) she may be teaching at Oxford University.

I don't understand that if we put ing form with modals then what sense they make.
I don't know what the meaning of "could not be leading" is.In other words what attitude is shown by these words. :?
Please make me clear this thing.I shall be very thankful to you.

Sonia*

[Torsten]

Hi Sonja,

Can you please help us by reading and following these instructions: What is a meaningful message title and why is it important?

TOEIC listening, photographs: The cyclists

[Sonia*]

I am sorry sir.

[Alan]

Hi Sonia,

You are right in saying that these modals are 'defective' because they don't have a complete set of verb parts. The characteristic of them all is that the verb following them has to be in the infinitive form whereas many verbs can be followed by either the infinitive or the 'ing' form as for example - begin to speak/begin speaking and so on. In your example 'could not be leading' the meaning is 'would not be able to be leading'. After 'could' comes the infinitive form 'be'. Similarly 'could not have believed' the verb following 'could' is the infinitive form 'have'. This means that the modal can introduce either a continuous form (be leading) or a perfect form (have believed).

Alan
_________________
English as a Second Language
You can read my ESL story Present Simple

[Torsten]