I can observe you can observe he can observe we can observe you can observe they can observe
V-ing form
I can be observing you can be observing he can be observing we can be observing you can be observing they can be observing
Perfect
I can have observed you can have observed he can have observed we can have observed you can have observed they can have observed
V-ing perfect
I can have been observing you can have been observing he can have been observing we can have been observing you can have been observing they can have been observing
Negation
Simple form
I cannot observe you cannot observe he cannot observe we cannot observe you cannot observe they cannot observe
V-ing form
I cannot be observing you cannot be observing he cannot be observing we cannot be observing you cannot be observing they cannot be observing
Perfect
I cannot have observed you cannot have observed he cannot have observed we cannot have observed you cannot have observed they cannot have observed
V-ing perfect
I cannot have been observing you cannot have been observing he cannot have been observing we cannot have been observing you cannot have been observing they cannot have been observing
Interrogative form
Simple form
can I observe? can you observe? can he observe? can we observe? can you observe? can they observe?
V-ing form
can I be observing? can you be observing? can he be observing? can we be observing? can you be observing? can they be observing?
Perfect
can I have observed? can you have observed? can he have observed? can we have observed? can you have observed? can they have observed?
V-ing perfect
can I have been observing? can you have been observing? can he have been observing? can we have been observing? can you have been observing? can they have been observing?
Interro-negative form
Simple form
can I not observe? can you not observe? can he not observe? can we not observe? can you not observe? can they not observe?
V-ing form
can I not be observing? can you not be observing? can he not be observing? can we not be observing? can you not be observing? can they not be observing?
Perfect
can I not have observed? can you not have observed? can he not have observed? can we not have observed? can you not have observed? can they not have observed?
V-ing perfect
can I not have been observing? can you not have been observing? can he not have been observing? can we not have been observing? can you not have been observing? can they not have been observing?