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 could not tiff you could not tiff he could not tiff we could not tiff you could not tiff they could not tiff	I could not be tiffing you could not be tiffing he could not be tiffing we could not be tiffing you could not be tiffing they could not be tiffing
Perfect	V-ing perfect
I could not have tiffed you could not have tiffed he could not have tiffed we could not have tiffed you could not have tiffed they could not have tiffed	I could not have been tiffing you could not have been tiffing he could not have been tiffing we could not have been tiffing you could not have been tiffing they could not 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
could I not tiff? could you not tiff? could he not tiff? could we not tiff? could you not tiff? could they not tiff?	could I not be tiffing? could you not be tiffing? could he not be tiffing? could we not be tiffing? could you not be tiffing? could they not be tiffing?
Perfect	V-ing perfect
could I not have tiffed? could you not have tiffed? could he not have tiffed? could we not have tiffed? could you not have tiffed? could they not have tiffed?	could I not have been tiffing? could you not have been tiffing? could he not have been tiffing? could we not have been tiffing? could you not have been tiffing? could they not have been tiffing?