In “I am running.”, isn’t running suppose to be a subject complement?

There’s a subtle distinction that makes “running” not a subject complement in “I am running.”

Here’s the key:

Linking verbs vs. auxiliary verbs:

While “am” is often a linking verb (e.g., “I am happy”), it can also function as an auxiliary verb (also called a helping verb). Auxiliary verbs combine with main verbs to form different tenses and moods.

Present continuous tense:

In “I am running,” the verb “am” is acting as an auxiliary verb. It’s working with the present participle “running” to create the present continuous tense, which describes an ongoing action.

Think of it this way:

Subject complement: “I am a runner” (“runner” renames the subject “I”)
Verb phrase (present continuous): “I am running” (“am running” describes the action in progress)

Even though the structure looks similar, the function of “am” changes, which affects the role of “running.”