Sometimes it is difficult to distinguish between a present participle and a gerund, since gerunds can also be used as adjectives. For example, in the phrase ''swimming pool'' the word ''swimming'' is a gerund used as an adjective. We know this because ''swimming pool'' means ''pool that is used for the activity of swimming.'' It is not a present participle because the pool is not doing the action of swimming. To see the difference, compare these two sentences:
