English verb conjugation
COULD STUMBLE

Regular verb: stumble - stumbled - stumbled

Affirmation

Simple form	V-ing form
I could stumble you could stumble he could stumble we could stumble you could stumble they could stumble	I could be stumbling you could be stumbling he could be stumbling we could be stumbling you could be stumbling they could be stumbling
Perfect	V-ing perfect
I could have stumbled you could have stumbled he could have stumbled we could have stumbled you could have stumbled they could have stumbled	I could have been stumbling you could have been stumbling he could have been stumbling we could have been stumbling you could have been stumbling they could have been stumbling

Negation

Simple form	V-ing form
I couldn't stumble you couldn't stumble he couldn't stumble we couldn't stumble you couldn't stumble they couldn't stumble	I couldn't be stumbling you couldn't be stumbling he couldn't be stumbling we couldn't be stumbling you couldn't be stumbling they couldn't be stumbling
Perfect	V-ing perfect
I couldn't have stumbled you couldn't have stumbled he couldn't have stumbled we couldn't have stumbled you couldn't have stumbled they couldn't have stumbled	I couldn't have been stumbling you couldn't have been stumbling he couldn't have been stumbling we couldn't have been stumbling you couldn't have been stumbling they couldn't have been stumbling

Interrogative form

Simple form	V-ing form
could I stumble? could you stumble? could he stumble? could we stumble? could you stumble? could they stumble?	could I be stumbling? could you be stumbling? could he be stumbling? could we be stumbling? could you be stumbling? could they be stumbling?
Perfect	V-ing perfect
could I have stumbled? could you have stumbled? could he have stumbled? could we have stumbled? could you have stumbled? could they have stumbled?	could I have been stumbling? could you have been stumbling? could he have been stumbling? could we have been stumbling? could you have been stumbling? could they have been stumbling?

Interro-negative form

Simple form	V-ing form
couldn't I stumble? couldn't you stumble? couldn't he stumble? couldn't we stumble? couldn't you stumble? couldn't they stumble?	couldn't I be stumbling? couldn't you be stumbling? couldn't he be stumbling? couldn't we be stumbling? couldn't you be stumbling? couldn't they be stumbling?
Perfect	V-ing perfect
couldn't I have stumbled? couldn't you have stumbled? couldn't he have stumbled? couldn't we have stumbled? couldn't you have stumbled? couldn't they have stumbled?	couldn't I have been stumbling? couldn't you have been stumbling? couldn't he have been stumbling? couldn't we have been stumbling? couldn't you have been stumbling? couldn't they have been stumbling?