What is the difference between the wave model and the tree model of language change diffusion?

• A. Wave model describes gradual diffusion across a speech community; Tree model describes divergence into distinct varieties.
• B. Wave model describes rapid global adoption; Tree model describes convergence of dialects.
• C. Wave model describes no diffusion; Tree model describes uniform language.
• D. Wave model describes only spelling changes; Tree model describes only phonology.

Answer: (A)

This question is about how linguists imagine the spread of language changes. The wave model sees diffusion as a gradual spread across a speech community: an innovation starts in one area or group and gradually influences neighboring speakers, so related features appear in a band or ripple-like pattern rather than across everyone all at once. It emphasizes social networks and proximity, with changes often spreading over time while still allowing variation to persist elsewhere.

The tree model, in contrast, treats language change as branching into distinct varieties over time. Features diverge as populations become more isolated or follow separate paths, leading to separate languages or dialect groups rather than widespread, uniform adoption. Diffusion across branches is limited, so changes tend to stay within a lineage rather than sweeping through the whole family.

So the main distinction is gradual, networked diffusion within a community (wave) versus bifurcation into separate lineages with more independent evolution (tree).

If you’re weighing the other ideas, they don’t fit because rapid global adoption isn’t the wave model’s typical pattern, convergence of dialects isn’t the tree model’s focus, and neither model describes no diffusion or only spelling/phonology in the way these options suggest.