It does not appear to be the case that the “di” in “dialectic” (unlike, say, the “di” in “dilemma”) refers to the number “two”. According to Etymonline and many

It does not appear to be the case that the “di” in “dialectic” (unlike, say, the “di” in “dilemma”) refers to the number “two”. According to Etymonline and many other dictionaries (follow links from https://www.onelook.com/?w=dialectic https://www.onelook.com/?w=dialectic), the word comes via Latin ultimately from Greek dialektos, “discourse, conversation”. This in turn is formed with the prefix dia- (“across, between”), also found in words like diagonal, diameter, dialogue, diagnosis, adiabatic, diabetes, diarrhea, diacritic. This prefix dia- in turn may indeed be cognate with bi or di-, but at any rate the “di” in “dialectic” does not directly refer to “two”. What you've read may be a later re-analysis / false etymology.