could sharpen
Regular verb: sharpen - sharpened- sharpened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could sharpen
you could sharpen
she could sharpen
we could sharpen
you could sharpen
they could sharpen 	I could be sharpening
you could be sharpening
she could be sharpening
we could be sharpening
you could be sharpening
they could be sharpening	I could have sharpened
you could have sharpened
she could have sharpened
we could have sharpened
you could have sharpened
they could have sharpened	I could have been sharpening
you could have been sharpening
she could have been sharpening
we could have been sharpening
you could have been sharpening
they could have been sharpening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't sharpen
you couldn't sharpen
she couldn't sharpen
we couldn't sharpen
you couldn't sharpen
they couldn't sharpen 	I couldn't be sharpening
you couldn't be sharpening
she couldn't be sharpening
we couldn't be sharpening
you couldn't be sharpening
they couldn't be sharpening	I couldn't have sharpened
you couldn't have sharpened
she couldn't have sharpened
we couldn't have sharpened
you couldn't have sharpened
they couldn't have sharpened	I couldn't have been sharpening
you couldn't have been sharpening
she couldn't have been sharpening
we couldn't have been sharpening
you couldn't have been sharpening
they couldn't have been sharpening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I sharpen?
could you sharpen?
could she sharpen?
could we sharpen?
could you sharpen?
could they sharpen? 	could I be sharpening?
could you be sharpening?
could she be sharpening?
could we be sharpening?
could you be sharpening?
could they be sharpening? 	could I have sharpened?
could you have sharpened?
could she have sharpened?
could we have sharpened?
could you have sharpened?
could they have sharpened? 	could I have been sharpening?
could you have been sharpening?
could she have been sharpening?
could we have been sharpening?
could you have been sharpening?
could they have been sharpening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I sharpen?
couldn't you sharpen?
couldn't she sharpen?
couldn't we sharpen?
couldn't you sharpen?
couldn't they sharpen? 	couldn't I be sharpening?
couldn't you be sharpening?
couldn't she be sharpening?
couldn't we be sharpening?
couldn't you be sharpening?
couldn't they be sharpening? 	couldn't I have sharpened?
couldn't you have sharpened?
couldn't she have sharpened?
couldn't we have sharpened?
couldn't you have sharpened?
couldn't they have sharpened? 	couldn't I have been sharpening?
couldn't you have been sharpening?
couldn't she have been sharpening?
couldn't we have been sharpening?
couldn't you have been sharpening?
couldn't they have been sharpening?