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