English verb conjugation
COULD THUMB

Regular verb: thumb - thumbed - thumbed

Affirmation

Simple form	V-ing form
I could thumb you could thumb he could thumb we could thumb you could thumb they could thumb	I could be thumbing you could be thumbing he could be thumbing we could be thumbing you could be thumbing they could be thumbing
Perfect	V-ing perfect
I could have thumbed you could have thumbed he could have thumbed we could have thumbed you could have thumbed they could have thumbed	I could have been thumbing you could have been thumbing he could have been thumbing we could have been thumbing you could have been thumbing they could have been thumbing

Negation

Simple form	V-ing form
I could not thumb you could not thumb he could not thumb we could not thumb you could not thumb they could not thumb	I could not be thumbing you could not be thumbing he could not be thumbing we could not be thumbing you could not be thumbing they could not be thumbing
Perfect	V-ing perfect
I could not have thumbed you could not have thumbed he could not have thumbed we could not have thumbed you could not have thumbed they could not have thumbed	I could not have been thumbing you could not have been thumbing he could not have been thumbing we could not have been thumbing you could not have been thumbing they could not have been thumbing

Interrogative form

Simple form	V-ing form
could I thumb? could you thumb? could he thumb? could we thumb? could you thumb? could they thumb?	could I be thumbing? could you be thumbing? could he be thumbing? could we be thumbing? could you be thumbing? could they be thumbing?
Perfect	V-ing perfect
could I have thumbed? could you have thumbed? could he have thumbed? could we have thumbed? could you have thumbed? could they have thumbed?	could I have been thumbing? could you have been thumbing? could he have been thumbing? could we have been thumbing? could you have been thumbing? could they have been thumbing?

Interro-negative form

Simple form	V-ing form
could I not thumb? could you not thumb? could he not thumb? could we not thumb? could you not thumb? could they not thumb?	could I not be thumbing? could you not be thumbing? could he not be thumbing? could we not be thumbing? could you not be thumbing? could they not be thumbing?
Perfect	V-ing perfect
could I not have thumbed? could you not have thumbed? could he not have thumbed? could we not have thumbed? could you not have thumbed? could they not have thumbed?	could I not have been thumbing? could you not have been thumbing? could he not have been thumbing? could we not have been thumbing? could you not have been thumbing? could they not have been thumbing?