I could decrease you could decrease he could decrease we could decrease you could decrease they could decrease
V-ing form
I could be decreasing you could be decreasing he could be decreasing we could be decreasing you could be decreasing they could be decreasing
Perfect
I could have decreased you could have decreased he could have decreased we could have decreased you could have decreased they could have decreased
V-ing perfect
I could have been decreasing you could have been decreasing he could have been decreasing we could have been decreasing you could have been decreasing they could have been decreasing
Negation
Simple form
I could not decrease you could not decrease he could not decrease we could not decrease you could not decrease they could not decrease
V-ing form
I could not be decreasing you could not be decreasing he could not be decreasing we could not be decreasing you could not be decreasing they could not be decreasing
Perfect
I could not have decreased you could not have decreased he could not have decreased we could not have decreased you could not have decreased they could not have decreased
V-ing perfect
I could not have been decreasing you could not have been decreasing he could not have been decreasing we could not have been decreasing you could not have been decreasing they could not have been decreasing
Interrogative form
Simple form
could I decrease? could you decrease? could he decrease? could we decrease? could you decrease? could they decrease?
V-ing form
could I be decreasing? could you be decreasing? could he be decreasing? could we be decreasing? could you be decreasing? could they be decreasing?
Perfect
could I have decreased? could you have decreased? could he have decreased? could we have decreased? could you have decreased? could they have decreased?
V-ing perfect
could I have been decreasing? could you have been decreasing? could he have been decreasing? could we have been decreasing? could you have been decreasing? could they have been decreasing?
Interro-negative form
Simple form
could I not decrease? could you not decrease? could he not decrease? could we not decrease? could you not decrease? could they not decrease?
V-ing form
could I not be decreasing? could you not be decreasing? could he not be decreasing? could we not be decreasing? could you not be decreasing? could they not be decreasing?
Perfect
could I not have decreased? could you not have decreased? could he not have decreased? could we not have decreased? could you not have decreased? could they not have decreased?
V-ing perfect
could I not have been decreasing? could you not have been decreasing? could he not have been decreasing? could we not have been decreasing? could you not have been decreasing? could they not have been decreasing?