English verb conjugation
COULD TIFF

Regular verb: tiff - tiffed - tiffed

Affirmation

Simple form	V-ing form
I could tiff you could tiff he could tiff we could tiff you could tiff they could tiff	I could be tiffing you could be tiffing he could be tiffing we could be tiffing you could be tiffing they could be tiffing
Perfect	V-ing perfect
I could have tiffed you could have tiffed he could have tiffed we could have tiffed you could have tiffed they could have tiffed	I could have been tiffing you could have been tiffing he could have been tiffing we could have been tiffing you could have been tiffing they could have been tiffing

Negation

Simple form	V-ing form
I couldn't tiff you couldn't tiff he couldn't tiff we couldn't tiff you couldn't tiff they couldn't tiff	I couldn't be tiffing you couldn't be tiffing he couldn't be tiffing we couldn't be tiffing you couldn't be tiffing they couldn't be tiffing
Perfect	V-ing perfect
I couldn't have tiffed you couldn't have tiffed he couldn't have tiffed we couldn't have tiffed you couldn't have tiffed they couldn't have tiffed	I couldn't have been tiffing you couldn't have been tiffing he couldn't have been tiffing we couldn't have been tiffing you couldn't have been tiffing they couldn't have been tiffing

Interrogative form

Simple form	V-ing form
could I tiff? could you tiff? could he tiff? could we tiff? could you tiff? could they tiff?	could I be tiffing? could you be tiffing? could he be tiffing? could we be tiffing? could you be tiffing? could they be tiffing?
Perfect	V-ing perfect
could I have tiffed? could you have tiffed? could he have tiffed? could we have tiffed? could you have tiffed? could they have tiffed?	could I have been tiffing? could you have been tiffing? could he have been tiffing? could we have been tiffing? could you have been tiffing? could they have been tiffing?

Interro-negative form

Simple form	V-ing form
couldn't I tiff? couldn't you tiff? couldn't he tiff? couldn't we tiff? couldn't you tiff? couldn't they tiff?	couldn't I be tiffing? couldn't you be tiffing? couldn't he be tiffing? couldn't we be tiffing? couldn't you be tiffing? couldn't they be tiffing?
Perfect	V-ing perfect
couldn't I have tiffed? couldn't you have tiffed? couldn't he have tiffed? couldn't we have tiffed? couldn't you have tiffed? couldn't they have tiffed?	couldn't I have been tiffing? couldn't you have been tiffing? couldn't he have been tiffing? couldn't we have been tiffing? couldn't you have been tiffing? couldn't they have been tiffing?