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