Syntax


Morphological properties


I. Modal auxiliaries and periphrastic do have defective paradigms:

(a) modal auxiliaries have no:

(i) infinitive, e.g. * to can
(ii) imperative, e.g. * Can!
(iii) participle, e.g. * is canning/has could
(iv) agreement marking on the 3rd person singular form, e.g. * she cans

(b) periphrastic do has

(i) no infinitive, * He tried to do not sleep
(ii) no participle, * is doing not sleep
(iii) an imperative, Do (not) leave!
(iv) agreement marking on the 3rd person singular form, Does he sleep?
(BUT: main verb do does have infinitival and participial forms, He has done so. He tried to do so.)

II. Auxiliary have and be have complete morphological paradigms.

THUS:
Modal auxiliaries, auxiliary have and be, and periphrastic do form three different morphological paradigms.