English verb conjugation
COULD STRENGTHEN

Regular verb: strengthen - strengthened - strengthened

Affirmation

Simple form	V-ing form
I could strengthen you could strengthen he could strengthen we could strengthen you could strengthen they could strengthen	I could be strengthening you could be strengthening he could be strengthening we could be strengthening you could be strengthening they could be strengthening
Perfect	V-ing perfect
I could have strengthened you could have strengthened he could have strengthened we could have strengthened you could have strengthened they could have strengthened	I could have been strengthening you could have been strengthening he could have been strengthening we could have been strengthening you could have been strengthening they could have been strengthening

Negation

Simple form	V-ing form
I couldn't strengthen you couldn't strengthen he couldn't strengthen we couldn't strengthen you couldn't strengthen they couldn't strengthen	I couldn't be strengthening you couldn't be strengthening he couldn't be strengthening we couldn't be strengthening you couldn't be strengthening they couldn't be strengthening
Perfect	V-ing perfect
I couldn't have strengthened you couldn't have strengthened he couldn't have strengthened we couldn't have strengthened you couldn't have strengthened they couldn't have strengthened	I couldn't have been strengthening you couldn't have been strengthening he couldn't have been strengthening we couldn't have been strengthening you couldn't have been strengthening they couldn't have been strengthening

Interrogative form

Simple form	V-ing form
could I strengthen? could you strengthen? could he strengthen? could we strengthen? could you strengthen? could they strengthen?	could I be strengthening? could you be strengthening? could he be strengthening? could we be strengthening? could you be strengthening? could they be strengthening?
Perfect	V-ing perfect
could I have strengthened? could you have strengthened? could he have strengthened? could we have strengthened? could you have strengthened? could they have strengthened?	could I have been strengthening? could you have been strengthening? could he have been strengthening? could we have been strengthening? could you have been strengthening? could they have been strengthening?

Interro-negative form

Simple form	V-ing form
couldn't I strengthen? couldn't you strengthen? couldn't he strengthen? couldn't we strengthen? couldn't you strengthen? couldn't they strengthen?	couldn't I be strengthening? couldn't you be strengthening? couldn't he be strengthening? couldn't we be strengthening? couldn't you be strengthening? couldn't they be strengthening?
Perfect	V-ing perfect
couldn't I have strengthened? couldn't you have strengthened? couldn't he have strengthened? couldn't we have strengthened? couldn't you have strengthened? couldn't they have strengthened?	couldn't I have been strengthening? couldn't you have been strengthening? couldn't he have been strengthening? couldn't we have been strengthening? couldn't you have been strengthening? couldn't they have been strengthening?