Swim:Used in the present tense (e.g., "I swim") and as an infinitive (e.g., "I want to swim"). Swam:Used in the simple past tense (e.g., "I swam yesterday"). Swum:Used in perfect tenses (e.g., "I have swum" or "I had swum") and in passive voice constructions. Swimming:Used as the present participle (e.g., "I am swimming") and as a gerund (e.g., "Swimming is good exercise").