I could differentiate you could differentiate she could differentiate we could differentiate you could differentiate they could differentiate
V-ing form
I could be differentiating you could be differentiating she could be differentiating we could be differentiating you could be differentiating they could be differentiating
Perfect
I could have differentiated you could have differentiated she could have differentiated we could have differentiated you could have differentiated they could have differentiated
V-ing perfect
I could have been differentiating you could have been differentiating she could have been differentiating we could have been differentiating you could have been differentiating they could have been differentiating
Negation
Simple form
I couldn't differentiate you couldn't differentiate she couldn't differentiate we couldn't differentiate you couldn't differentiate they couldn't differentiate
V-ing form
I couldn't be differentiating you couldn't be differentiating she couldn't be differentiating we couldn't be differentiating you couldn't be differentiating they couldn't be differentiating
Perfect
I couldn't have differentiated you couldn't have differentiated she couldn't have differentiated we couldn't have differentiated you couldn't have differentiated they couldn't have differentiated
V-ing perfect
I couldn't have been differentiating you couldn't have been differentiating she couldn't have been differentiating we couldn't have been differentiating you couldn't have been differentiating they couldn't have been differentiating
Interrogative form
Simple form
could I differentiate? could you differentiate? could she differentiate? could we differentiate? could you differentiate? could they differentiate?
V-ing form
could I be differentiating? could you be differentiating? could she be differentiating? could we be differentiating? could you be differentiating? could they be differentiating?
Perfect
could I have differentiated? could you have differentiated? could she have differentiated? could we have differentiated? could you have differentiated? could they have differentiated?
V-ing perfect
could I have been differentiating? could you have been differentiating? could she have been differentiating? could we have been differentiating? could you have been differentiating? could they have been differentiating?
Interro-negative form
Simple form
couldn't I differentiate? couldn't you differentiate? couldn't she differentiate? couldn't we differentiate? couldn't you differentiate? couldn't they differentiate?
V-ing form
couldn't I be differentiating? couldn't you be differentiating? couldn't she be differentiating? couldn't we be differentiating? couldn't you be differentiating? couldn't they be differentiating?
Perfect
couldn't I have differentiated? couldn't you have differentiated? couldn't she have differentiated? couldn't we have differentiated? couldn't you have differentiated? couldn't they have differentiated?
V-ing perfect
couldn't I have been differentiating? couldn't you have been differentiating? couldn't she have been differentiating? couldn't we have been differentiating? couldn't you have been differentiating? couldn't they have been differentiating?