How Big is Your Vocabulary?

I often see descriptions of how much vocabulary is necessary for each level of ability in a language. Focusing on vocabulary, however, is often a mistake. One of the biggest issues is: how do we quantify words? Let's look at an example:

1. I run races
2. The dog runs
3. He runs a company
4. They ran away
5. Running is fun
6. The dog is running
7. Don't run from your past
8. She went for a run
9. He's got the runs
10. This egg is runny
11. The river runs through the town
12. The place was run down
13. We ran up a huge tab
14. She's a marathon runner
15. He's a drug runner

So, what is a word? Here are 15 different variations on the word run. Some are nouns, some are adjectives, and some are verbs. Phrasal verbs (connected idiomatically with a preposition) are based on the verb to run, but have completely different meanings. So, how many words do we have here?

Running could be a noun — as in Running is fun — or an adjective — as in the running dog. The form is identical but the meaning and function are different. Are these two separate words? Does running up a tab use a different "word" to running up a hill?

This is why having the core set of patterns and structures is so important. You could find more examples of uses of the verb to run. With 10 "words" like run, you could have a vocabulary of 150 or more different meanings. So, what are you going to count as a word?