English verb conjugation
COULD TOUGHEN

Regular verb: toughen - toughened - toughened

Affirmation

Simple form	V-ing form
I could toughen you could toughen he could toughen we could toughen you could toughen they could toughen	I could be toughening you could be toughening he could be toughening we could be toughening you could be toughening they could be toughening
Perfect	V-ing perfect
I could have toughened you could have toughened he could have toughened we could have toughened you could have toughened they could have toughened	I could have been toughening you could have been toughening he could have been toughening we could have been toughening you could have been toughening they could have been toughening

Negation

Simple form	V-ing form
I couldn't toughen you couldn't toughen he couldn't toughen we couldn't toughen you couldn't toughen they couldn't toughen	I couldn't be toughening you couldn't be toughening he couldn't be toughening we couldn't be toughening you couldn't be toughening they couldn't be toughening
Perfect	V-ing perfect
I couldn't have toughened you couldn't have toughened he couldn't have toughened we couldn't have toughened you couldn't have toughened they couldn't have toughened	I couldn't have been toughening you couldn't have been toughening he couldn't have been toughening we couldn't have been toughening you couldn't have been toughening they couldn't have been toughening

Interrogative form

Simple form	V-ing form
could I toughen? could you toughen? could he toughen? could we toughen? could you toughen? could they toughen?	could I be toughening? could you be toughening? could he be toughening? could we be toughening? could you be toughening? could they be toughening?
Perfect	V-ing perfect
could I have toughened? could you have toughened? could he have toughened? could we have toughened? could you have toughened? could they have toughened?	could I have been toughening? could you have been toughening? could he have been toughening? could we have been toughening? could you have been toughening? could they have been toughening?

Interro-negative form

Simple form	V-ing form
couldn't I toughen? couldn't you toughen? couldn't he toughen? couldn't we toughen? couldn't you toughen? couldn't they toughen?	couldn't I be toughening? couldn't you be toughening? couldn't he be toughening? couldn't we be toughening? couldn't you be toughening? couldn't they be toughening?
Perfect	V-ing perfect
couldn't I have toughened? couldn't you have toughened? couldn't he have toughened? couldn't we have toughened? couldn't you have toughened? couldn't they have toughened?	couldn't I have been toughening? couldn't you have been toughening? couldn't he have been toughening? couldn't we have been toughening? couldn't you have been toughening? couldn't they have been toughening?