Plutarch was born in Chaeronea of Boeotia around 50 AD during the reign of the Roman Emperor Claudius. He was the son of Aristobulus, a biographer and philosopher. Coming from a distinguished family, he received a well-rounded education, studying mathematics and philosophy in Athens, with the philosopher Ammonius as his teacher during that period at the Academy in Athens.

He was a significant historian, biographer, and philosopher. In the orthography of the time, which still follows that of the Attic inscriptions of the 5th century, the letter E, the fifth of the alphabet, is similarly noted with the diphthong ει. Therefore, the interpretations suggested for the Delphic E include the conjunction εἰ and the verbal form εἶ.

The explanations provided are as follows:

1. The E is a dedication, an offering from the Wise to remind that it is 5 and not 7.
2. The E, the second vowel in the sequence of the alphabet, could symbolize the sun, as it holds the second position among the planets, and since Apollo is identified with it, the E may be the symbol of the god of Delphi.
3. The εἰ, which means "if," as an interrogative conjunction, is referred to by those approaching for oracular consultation, as they pose their question to the Pythia.
4. The εἰ, as a hypothetical conjunction, is necessary in every reasoning process, as Apollo is the god of philosophy and dialectics.
5. The conjunction εἰ as εἴθε and as εἰ γὰρ has a wishful meaning, expressing a hope.
6. The number 5 is symbolized by the E, having significance for mathematics, for matters of the soul, and finally for music.
7. Εἶ means that you are, being the primary way of greeting the god upon entering the temple.