A few years ago, I was introduced by Greg Stump to the notion of distinguishers in morphological description. The analysis of inflected forms in terms of theme + distinguisher is a very helpful concept and one that is made use extensively in my ongoing work on New Testament Greek morphology.

Take a word like φιλοῦμεν. The underlying stem is φιλε and the suffix is ομεν. The sandhi rule ε + ο → ου has been applied.

So in the surface form of the word, the φιλ is part but not all of the stem. It’s the part that will likely (unless there is suppletion) be common with other cells in the paradigm. Similarly οῦμεν is not the suffix but it is the part that is indicating “first person plural” (as well as indicating that the stem likely ends in ε or ο).

Stump calls φιλ the theme and οῦμεν the distinguisher. The theme is what the cells in a paradigm have in common, the distinguisher is what distinguishes them from one another.

SPOILER ALERT: I’m working on a full theme/distinguisher and stem/suffix analysis of every inflected form in the Greek New Testament as part of my Morphological Lexicon of New Testament Greek.