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or running (this can occur as the answer to a question such as What is he doing?). A form that cannot occur in isolation is a bound form, e.g. -y, is, and -ing (in Johnny is running). Non-occurrence in isolation is given as the primary criterion for boundness in most linguistics textbooks.

Roots and affixes

Affixes are bound by definition. English language affixes are almost exclusively prefixes or suffixes:

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