I could inquire you could inquire he could inquire we could inquire you could inquire they could inquire
V-ing form
I could be inquiring you could be inquiring he could be inquiring we could be inquiring you could be inquiring they could be inquiring
Perfect
I could have inquired you could have inquired he could have inquired we could have inquired you could have inquired they could have inquired
V-ing perfect
I could have been inquiring you could have been inquiring he could have been inquiring we could have been inquiring you could have been inquiring they could have been inquiring
Negation
Simple form
I couldn't inquire you couldn't inquire he couldn't inquire we couldn't inquire you couldn't inquire they couldn't inquire
V-ing form
I couldn't be inquiring you couldn't be inquiring he couldn't be inquiring we couldn't be inquiring you couldn't be inquiring they couldn't be inquiring
Perfect
I couldn't have inquired you couldn't have inquired he couldn't have inquired we couldn't have inquired you couldn't have inquired they couldn't have inquired
V-ing perfect
I couldn't have been inquiring you couldn't have been inquiring he couldn't have been inquiring we couldn't have been inquiring you couldn't have been inquiring they couldn't have been inquiring
Interrogative form
Simple form
could I inquire? could you inquire? could he inquire? could we inquire? could you inquire? could they inquire?
V-ing form
could I be inquiring? could you be inquiring? could he be inquiring? could we be inquiring? could you be inquiring? could they be inquiring?
Perfect
could I have inquired? could you have inquired? could he have inquired? could we have inquired? could you have inquired? could they have inquired?
V-ing perfect
could I have been inquiring? could you have been inquiring? could he have been inquiring? could we have been inquiring? could you have been inquiring? could they have been inquiring?
Interro-negative form
Simple form
couldn't I inquire? couldn't you inquire? couldn't he inquire? couldn't we inquire? couldn't you inquire? couldn't they inquire?
V-ing form
couldn't I be inquiring? couldn't you be inquiring? couldn't he be inquiring? couldn't we be inquiring? couldn't you be inquiring? couldn't they be inquiring?
Perfect
couldn't I have inquired? couldn't you have inquired? couldn't he have inquired? couldn't we have inquired? couldn't you have inquired? couldn't they have inquired?
V-ing perfect
couldn't I have been inquiring? couldn't you have been inquiring? couldn't he have been inquiring? couldn't we have been inquiring? couldn't you have been inquiring? couldn't they have been inquiring?