Historical Linguistics and Language Families 5, Exercise 3: three counts

What the sources say: Ethnologue counts 7,151 living languages in 142
families; Campbell (2019) counts 406 independent families including isolates;
Glottolog counts 423, with 184 isolates.

Reasons suggested:
  1. The counts use different methods; Ethnologue's smaller figure suggests
     it groups more languages together (this chapter's inference, not the
     source's statement).
  2. The counts treat isolates and unproven relationships differently. The
     Language family page defines an isolate as a language with no proven
     relatives, and Glottolog's figure of 423 includes 184 of them.

To trust one, find out:
  - how each source decides that two languages are related (the evidence it
    requires, e.g. the comparative method of Chapter 3);
  - how each counts isolates and unclassified languages;
  - the date of each edition (the pages show Ethnologue 27 from 2024 and
    Glottolog 5.3 from 2026, and the Indo-European page gives an older
    Ethnologue figure of 446 languages against 454).