I could quicken you could quicken he could quicken we could quicken you could quicken they could quicken
V-ing form
I could be quickening you could be quickening he could be quickening we could be quickening you could be quickening they could be quickening
Perfect
I could have quickened you could have quickened he could have quickened we could have quickened you could have quickened they could have quickened
V-ing perfect
I could have been quickening you could have been quickening he could have been quickening we could have been quickening you could have been quickening they could have been quickening
Negation
Simple form
I couldn't quicken you couldn't quicken he couldn't quicken we couldn't quicken you couldn't quicken they couldn't quicken
V-ing form
I couldn't be quickening you couldn't be quickening he couldn't be quickening we couldn't be quickening you couldn't be quickening they couldn't be quickening
Perfect
I couldn't have quickened you couldn't have quickened he couldn't have quickened we couldn't have quickened you couldn't have quickened they couldn't have quickened
V-ing perfect
I couldn't have been quickening you couldn't have been quickening he couldn't have been quickening we couldn't have been quickening you couldn't have been quickening they couldn't have been quickening
Interrogative form
Simple form
could I quicken? could you quicken? could he quicken? could we quicken? could you quicken? could they quicken?
V-ing form
could I be quickening? could you be quickening? could he be quickening? could we be quickening? could you be quickening? could they be quickening?
Perfect
could I have quickened? could you have quickened? could he have quickened? could we have quickened? could you have quickened? could they have quickened?
V-ing perfect
could I have been quickening? could you have been quickening? could he have been quickening? could we have been quickening? could you have been quickening? could they have been quickening?
Interro-negative form
Simple form
couldn't I quicken? couldn't you quicken? couldn't he quicken? couldn't we quicken? couldn't you quicken? couldn't they quicken?
V-ing form
couldn't I be quickening? couldn't you be quickening? couldn't he be quickening? couldn't we be quickening? couldn't you be quickening? couldn't they be quickening?
Perfect
couldn't I have quickened? couldn't you have quickened? couldn't he have quickened? couldn't we have quickened? couldn't you have quickened? couldn't they have quickened?
V-ing perfect
couldn't I have been quickening? couldn't you have been quickening? couldn't he have been quickening? couldn't we have been quickening? couldn't you have been quickening? couldn't they have been quickening?