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 can't contribute you can't contribute he can't contribute we can't contribute you can't contribute they can't contribute
V-ing form
I can't be contributing you can't be contributing he can't be contributing we can't be contributing you can't be contributing they can't be contributing
Perfect
I can't have contributed you can't have contributed he can't have contributed we can't have contributed you can't have contributed they can't have contributed
V-ing perfect
I can't have been contributing you can't have been contributing he can't have been contributing we can't have been contributing you can't have been contributing they can't 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't I contribute? can't you contribute? can't he contribute? can't we contribute? can't you contribute? can't they contribute?
V-ing form
can't I be contributing? can't you be contributing? can't he be contributing? can't we be contributing? can't you be contributing? can't they be contributing?
Perfect
can't I have contributed? can't you have contributed? can't he have contributed? can't we have contributed? can't you have contributed? can't they have contributed?
V-ing perfect
can't I have been contributing? can't you have been contributing? can't he have been contributing? can't we have been contributing? can't you have been contributing? can't they have been contributing?