Questions & Answers about “Et” coniunctio est, et “sed” quoque coniunctio est.
Because the two ets are doing different jobs.
The first Et is being mentioned as a word. It means something like: the word et.
The second et is being used normally as a conjunction, so it means and and joins the two statements together.
So the pattern is like English:
And is a conjunction, and but is also a conjunction.
Coniunctio means conjunction.
It is the grammatical term for a word like et (and) or sed (but) that joins words, phrases, or clauses.