I can contribute you can contribute he can contribute we can contribute you can contribute they can contribute
V-ing form
I can be contributing you can be contributing he can be contributing we can be contributing you can be contributing they can be contributing
Perfect
I can have contributed you can have contributed he 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 he 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 he cannot contribute we cannot contribute you cannot contribute they cannot contribute
V-ing form
I cannot be contributing you cannot be contributing he cannot be contributing we cannot be contributing you cannot be contributing they cannot be contributing
Perfect
I cannot have contributed you cannot have contributed he 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 he 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 he contribute? can we contribute? can you contribute? can they contribute?
V-ing form
can I be contributing? can you be contributing? can he be contributing? can we be contributing? can you be contributing? can they be contributing?
Perfect
can I have contributed? can you have contributed? can he 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 he 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 he 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 he 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 he 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 he not have been contributing? can we not have been contributing? can you not have been contributing? can they not have been contributing?