Grammar: The Function of a Word
Words function in two ways. They label the things we talk about: the objects we see and think about. They explain the way in which those things connect. Our language and the order of words reflect the way the people who use the language think about those things and their connections. For decades we have talked about grammar in a way that doesn't make sense unless you are a grammarian or linguist. But that way of thinking is not the way we knowingly live with language.
We don't think of words as a thing belonging to a category: noun, pronoun, adjective, verb, adverb, preposition, or conjunction. We don't even think of words as participles. We think about life and use words to explain what we see.
Words happen to be used as nouns, pronouns, adjectives, verbs, adverbs, prepositions, or conjunctions. Depending on the life of the word, a word can be used in more than one way. Run is most often thought of as a motion, but it can be thought of in more than one way.
When we think of run as a motion, we use run as a verb. (e.g., Dogs run in the park.)
When we think of run as an object, we use run as a noun. (e.g., I set up a dog-run for my dog.)
When we think of run as a kind of something, we add -ing and use it as an adjective. (e.g., running water)
When we think of run as an experience, we use it as a past participle but don't change the spelling. (I have run two marathons.)
Run is something in the world, how we use it is called grammar.