I could masturbate you could masturbate he could masturbate we could masturbate you could masturbate they could masturbate
V-ing form
I could be masturbating you could be masturbating he could be masturbating we could be masturbating you could be masturbating they could be masturbating
Perfect
I could have masturbated you could have masturbated he could have masturbated we could have masturbated you could have masturbated they could have masturbated
V-ing perfect
I could have been masturbating you could have been masturbating he could have been masturbating we could have been masturbating you could have been masturbating they could have been masturbating
Negation
Simple form
I couldn't masturbate you couldn't masturbate he couldn't masturbate we couldn't masturbate you couldn't masturbate they couldn't masturbate
V-ing form
I couldn't be masturbating you couldn't be masturbating he couldn't be masturbating we couldn't be masturbating you couldn't be masturbating they couldn't be masturbating
Perfect
I couldn't have masturbated you couldn't have masturbated he couldn't have masturbated we couldn't have masturbated you couldn't have masturbated they couldn't have masturbated
V-ing perfect
I couldn't have been masturbating you couldn't have been masturbating he couldn't have been masturbating we couldn't have been masturbating you couldn't have been masturbating they couldn't have been masturbating
Interrogative form
Simple form
could I masturbate? could you masturbate? could he masturbate? could we masturbate? could you masturbate? could they masturbate?
V-ing form
could I be masturbating? could you be masturbating? could he be masturbating? could we be masturbating? could you be masturbating? could they be masturbating?
Perfect
could I have masturbated? could you have masturbated? could he have masturbated? could we have masturbated? could you have masturbated? could they have masturbated?
V-ing perfect
could I have been masturbating? could you have been masturbating? could he have been masturbating? could we have been masturbating? could you have been masturbating? could they have been masturbating?
Interro-negative form
Simple form
couldn't I masturbate? couldn't you masturbate? couldn't he masturbate? couldn't we masturbate? couldn't you masturbate? couldn't they masturbate?
V-ing form
couldn't I be masturbating? couldn't you be masturbating? couldn't he be masturbating? couldn't we be masturbating? couldn't you be masturbating? couldn't they be masturbating?
Perfect
couldn't I have masturbated? couldn't you have masturbated? couldn't he have masturbated? couldn't we have masturbated? couldn't you have masturbated? couldn't they have masturbated?
V-ing perfect
couldn't I have been masturbating? couldn't you have been masturbating? couldn't he have been masturbating? couldn't we have been masturbating? couldn't you have been masturbating? couldn't they have been masturbating?