The words people choose are not accidental. Vocabulary, nicknames, recurring phrases, formality level, and humor type are all fingerprints of how two people relate.
Nicknames and terms of address
What people call each other encodes intimacy level, power, and affection. A nickname that only two people share marks the boundary of the dyad.
Shared vocabulary
Words and phrases that appear in both people's messages indicate convergence. Lexical convergence is a measurable sign of closeness.
Formality register
How formal or casual the language is, and whether it matches between the two people, reveals the relationship's texture.
Humor type
Dark humor, absurdist humor, self-deprecating humor, sexual humor. Each type signals what the relationship can hold and what role humor plays in it.
Recurring phrases
Phrases that appear repeatedly across months often mark the relationship's core preoccupations, its running jokes, its fault lines.