εἰμί is the first person singular verb for “to be” (εἶναι [the infinitive form] = “to be”).

It an irregular verb, and, like English, changes significantly between person and tense. For example εἰμί is the word for am and ἦν is the word for was, e.g.

• ἐγώ εἰμι ὁ ποιμήν ὁ καλός… “I am the good shepherd.” (John 10:11)
• ὁ λόγος ἦν πρὸς τὸν θεόν… “The Word was with God.” (John 1:1)

The most common forms of “to be” in the New Testament are:

• ἐστίν - 3rd person singular present indicative, e.g. “it is” or “he is”, occurring around 900 times in the New Testament
• ἦν - 3rd person singular imperfective indicative - “it was” or “he was”
• εἰσίν or εἰσί - 3rd person plural present indicative - “they are”
• εἰμί - 1st person singular present indicative - “I am” - occurring around 140 times in the New Testament
• εἶναι (infinitive) - present infinitive - “to be”
• ἐσμέν - 1st person plural present indicative - “we are”
• ἐστέ - 2nd person plural present indicative - “you are”
• ἦμεν - 3rd person plural imperfect indicative - “we were”
• ἦσαν - 3rd person plural imperfect indicative - “they were”