I can investigate you can investigate he can investigate we can investigate you can investigate they can investigate
V-ing form
I can be investigating you can be investigating he can be investigating we can be investigating you can be investigating they can be investigating
Perfect
I can have investigated you can have investigated he can have investigated we can have investigated you can have investigated they can have investigated
V-ing perfect
I can have been investigating you can have been investigating he can have been investigating we can have been investigating you can have been investigating they can have been investigating
Negation
Simple form
I can't investigate you can't investigate he can't investigate we can't investigate you can't investigate they can't investigate
V-ing form
I can't be investigating you can't be investigating he can't be investigating we can't be investigating you can't be investigating they can't be investigating
Perfect
I can't have investigated you can't have investigated he can't have investigated we can't have investigated you can't have investigated they can't have investigated
V-ing perfect
I can't have been investigating you can't have been investigating he can't have been investigating we can't have been investigating you can't have been investigating they can't have been investigating
Interrogative form
Simple form
can I investigate? can you investigate? can he investigate? can we investigate? can you investigate? can they investigate?
V-ing form
can I be investigating? can you be investigating? can he be investigating? can we be investigating? can you be investigating? can they be investigating?
Perfect
can I have investigated? can you have investigated? can he have investigated? can we have investigated? can you have investigated? can they have investigated?
V-ing perfect
can I have been investigating? can you have been investigating? can he have been investigating? can we have been investigating? can you have been investigating? can they have been investigating?
Interro-negative form
Simple form
can't I investigate? can't you investigate? can't he investigate? can't we investigate? can't you investigate? can't they investigate?
V-ing form
can't I be investigating? can't you be investigating? can't he be investigating? can't we be investigating? can't you be investigating? can't they be investigating?
Perfect
can't I have investigated? can't you have investigated? can't he have investigated? can't we have investigated? can't you have investigated? can't they have investigated?
V-ing perfect
can't I have been investigating? can't you have been investigating? can't he have been investigating? can't we have been investigating? can't you have been investigating? can't they have been investigating?