I could string you could string she could string we could string you could string they could string
V-ing form
I could be stringing you could be stringing she could be stringing we could be stringing you could be stringing they could be stringing
Perfect
I could have strung you could have strung she could have strung we could have strung you could have strung they could have strung
V-ing perfect
I could have been stringing you could have been stringing she could have been stringing we could have been stringing you could have been stringing they could have been stringing
Negation
Simple form
I could not string you could not string she could not string we could not string you could not string they could not string
V-ing form
I could not be stringing you could not be stringing she could not be stringing we could not be stringing you could not be stringing they could not be stringing
Perfect
I could not have strung you could not have strung she could not have strung we could not have strung you could not have strung they could not have strung
V-ing perfect
I could not have been stringing you could not have been stringing she could not have been stringing we could not have been stringing you could not have been stringing they could not have been stringing
Interrogative form
Simple form
could I string? could you string? could she string? could we string? could you string? could they string?
V-ing form
could I be stringing? could you be stringing? could she be stringing? could we be stringing? could you be stringing? could they be stringing?
Perfect
could I have strung? could you have strung? could she have strung? could we have strung? could you have strung? could they have strung?
V-ing perfect
could I have been stringing? could you have been stringing? could she have been stringing? could we have been stringing? could you have been stringing? could they have been stringing?
Interro-negative form
Simple form
could I not string? could you not string? could she not string? could we not string? could you not string? could they not string?
V-ing form
could I not be stringing? could you not be stringing? could she not be stringing? could we not be stringing? could you not be stringing? could they not be stringing?
Perfect
could I not have strung? could you not have strung? could she not have strung? could we not have strung? could you not have strung? could they not have strung?
V-ing perfect
could I not have been stringing? could you not have been stringing? could she not have been stringing? could we not have been stringing? could you not have been stringing? could they not have been stringing?