There has been an age-long debate on the use of It is I/It is me and grammarians are still divided on which of them is correct or appropriate.
This argument centres on the rule of predicate nominative. The predicate nominative is a noun or pronoun at the object end of a linking verb.
Linking verbs are: is, was, am, has been, can be, will be, etc.
The rule is that the predicate nominative should be in the subject form even in object positions. So, we’d say:
- It is I.
- It was we.
This rule is based on Latin grammar, that’s why some English grammarians do not support it.
However, it’s natural for most of us (both native and non-native speakers) to say ‘It is me’. Thus, this is acceptable in our everyday informal conversations.
In essence, the use of It is I is generally formal while It is me is informal and more natural.