I can contribute you can contribute she can contribute we can contribute you can contribute they can contribute
V-ing form
I can be contributing you can be contributing she can be contributing we can be contributing you can be contributing they can be contributing
Perfect
I can have contributed you can have contributed she can have contributed we can have contributed you can have contributed they can have contributed
V-ing perfect
I can have been contributing you can have been contributing she can have been contributing we can have been contributing you can have been contributing they can have been contributing
Negation
Simple form
I cannot contribute you cannot contribute she cannot contribute we cannot contribute you cannot contribute they cannot contribute
V-ing form
I cannot be contributing you cannot be contributing she cannot be contributing we cannot be contributing you cannot be contributing they cannot be contributing
Perfect
I cannot have contributed you cannot have contributed she cannot have contributed we cannot have contributed you cannot have contributed they cannot have contributed
V-ing perfect
I cannot have been contributing you cannot have been contributing she cannot have been contributing we cannot have been contributing you cannot have been contributing they cannot have been contributing
Interrogative form
Simple form
can I contribute? can you contribute? can she contribute? can we contribute? can you contribute? can they contribute?
V-ing form
can I be contributing? can you be contributing? can she be contributing? can we be contributing? can you be contributing? can they be contributing?
Perfect
can I have contributed? can you have contributed? can she have contributed? can we have contributed? can you have contributed? can they have contributed?
V-ing perfect
can I have been contributing? can you have been contributing? can she have been contributing? can we have been contributing? can you have been contributing? can they have been contributing?
Interro-negative form
Simple form
can I not contribute? can you not contribute? can she not contribute? can we not contribute? can you not contribute? can they not contribute?
V-ing form
can I not be contributing? can you not be contributing? can she not be contributing? can we not be contributing? can you not be contributing? can they not be contributing?
Perfect
can I not have contributed? can you not have contributed? can she not have contributed? can we not have contributed? can you not have contributed? can they not have contributed?
V-ing perfect
can I not have been contributing? can you not have been contributing? can she not have been contributing? can we not have been contributing? can you not have been contributing? can they not have been contributing?