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