English verb conjugation
COULD THUMBTACK

Regular verb: thumbtack - thumbtacked - thumbtacked

Affirmation

Simple form	V-ing form
I could thumbtack you could thumbtack she could thumbtack we could thumbtack you could thumbtack they could thumbtack	I could be thumbtacking you could be thumbtacking she could be thumbtacking we could be thumbtacking you could be thumbtacking they could be thumbtacking
Perfect	V-ing perfect
I could have thumbtacked you could have thumbtacked she could have thumbtacked we could have thumbtacked you could have thumbtacked they could have thumbtacked	I could have been thumbtacking you could have been thumbtacking she could have been thumbtacking we could have been thumbtacking you could have been thumbtacking they could have been thumbtacking

Negation

Simple form	V-ing form
I couldn't thumbtack you couldn't thumbtack she couldn't thumbtack we couldn't thumbtack you couldn't thumbtack they couldn't thumbtack	I couldn't be thumbtacking you couldn't be thumbtacking she couldn't be thumbtacking we couldn't be thumbtacking you couldn't be thumbtacking they couldn't be thumbtacking
Perfect	V-ing perfect
I couldn't have thumbtacked you couldn't have thumbtacked she couldn't have thumbtacked we couldn't have thumbtacked you couldn't have thumbtacked they couldn't have thumbtacked	I couldn't have been thumbtacking you couldn't have been thumbtacking she couldn't have been thumbtacking we couldn't have been thumbtacking you couldn't have been thumbtacking they couldn't have been thumbtacking

Interrogative form

Simple form	V-ing form
could I thumbtack? could you thumbtack? could she thumbtack? could we thumbtack? could you thumbtack? could they thumbtack?	could I be thumbtacking? could you be thumbtacking? could she be thumbtacking? could we be thumbtacking? could you be thumbtacking? could they be thumbtacking?
Perfect	V-ing perfect
could I have thumbtacked? could you have thumbtacked? could she have thumbtacked? could we have thumbtacked? could you have thumbtacked? could they have thumbtacked?	could I have been thumbtacking? could you have been thumbtacking? could she have been thumbtacking? could we have been thumbtacking? could you have been thumbtacking? could they have been thumbtacking?

Interro-negative form

Simple form	V-ing form
couldn't I thumbtack? couldn't you thumbtack? couldn't she thumbtack? couldn't we thumbtack? couldn't you thumbtack? couldn't they thumbtack?	couldn't I be thumbtacking? couldn't you be thumbtacking? couldn't she be thumbtacking? couldn't we be thumbtacking? couldn't you be thumbtacking? couldn't they be thumbtacking?
Perfect	V-ing perfect
couldn't I have thumbtacked? couldn't you have thumbtacked? couldn't she have thumbtacked? couldn't we have thumbtacked? couldn't you have thumbtacked? couldn't they have thumbtacked?	couldn't I have been thumbtacking? couldn't you have been thumbtacking? couldn't she have been thumbtacking? couldn't we have been thumbtacking? couldn't you have been thumbtacking? couldn't they have been thumbtacking?