Consider these examples:
- cows eat grass
- cows eating grass
What about "cows eating grass"? This noun phrase could be a subject, but it has no predicate attached to it: the adjective phrase "eating grass" show which cows the writer is referring to, but there is nothing here to show why the writer is mentioning cows in the first place.
- cows eating grass are visible from the highway
This is a complete clause again. The subject "cows eating grass" and the predicate "are visible from the highway" make up a complete thought.
This single-word command is also a clause, even though it does seem to have a subject. With a direct command, it is not necessary to include the subject, since it is obviously the person or people you are talking to: in other words, the clause really reads "[You] run!". You should not usually use direct commands in your essays, except in quotations.
Written by David Megginson