Question

what is the difference between modals and non modal auxiliary verb​

Answer 1

$\small \bold \green{non - modals}$

➜ 3sg , infinitive participle forms

has, to have , having , had

is , to be , being , been

$\small \bold \green{modals}$

➜ do not have infinitival forms

to must

➜ do not inflect for 3sg

➜ do not have participle forms

musting(X) , musted(X)