I could attest you could attest he could attest we could attest you could attest they could attest
V-ing form
I could be attesting you could be attesting he could be attesting we could be attesting you could be attesting they could be attesting
Perfect
I could have attested you could have attested he could have attested we could have attested you could have attested they could have attested
V-ing perfect
I could have been attesting you could have been attesting he could have been attesting we could have been attesting you could have been attesting they could have been attesting
Negation
Simple form
I could not attest you could not attest he could not attest we could not attest you could not attest they could not attest
V-ing form
I could not be attesting you could not be attesting he could not be attesting we could not be attesting you could not be attesting they could not be attesting
Perfect
I could not have attested you could not have attested he could not have attested we could not have attested you could not have attested they could not have attested
V-ing perfect
I could not have been attesting you could not have been attesting he could not have been attesting we could not have been attesting you could not have been attesting they could not have been attesting
Interrogative form
Simple form
could I attest? could you attest? could he attest? could we attest? could you attest? could they attest?
V-ing form
could I be attesting? could you be attesting? could he be attesting? could we be attesting? could you be attesting? could they be attesting?
Perfect
could I have attested? could you have attested? could he have attested? could we have attested? could you have attested? could they have attested?
V-ing perfect
could I have been attesting? could you have been attesting? could he have been attesting? could we have been attesting? could you have been attesting? could they have been attesting?
Interro-negative form
Simple form
could I not attest? could you not attest? could he not attest? could we not attest? could you not attest? could they not attest?
V-ing form
could I not be attesting? could you not be attesting? could he not be attesting? could we not be attesting? could you not be attesting? could they not be attesting?
Perfect
could I not have attested? could you not have attested? could he not have attested? could we not have attested? could you not have attested? could they not have attested?
V-ing perfect
could I not have been attesting? could you not have been attesting? could he not have been attesting? could we not have been attesting? could you not have been attesting? could they not have been attesting?