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So what "Non‑Linguistic Factors" means is things that are not related to language learning directly. When we talk about language learning research, when we talk about the best methods to use when you learn English, those are linguistic factors, right? They are related to the language. Non‑linguistic factors means not related to the language. This has nothing to do with English, it's more about psychology. Motivation, for example, is a non‑linguistic factor. So that all it really means is just emotional factors. And there are actually many research studies about this topic.