1. Infinitive: This is the base form of the verb, usually preceded by "to." Examples: *to run*, *to eat*, *to sleep*.
2. Past Tense: This form describes an action that happened in the past. Examples: *ran*, *ate*, *slept*.
3. Past Participle: This form is used in perfect tenses (present perfect, past perfect, future perfect) and passive voice. Examples: *run*, *eaten*, *slept*.
4. Present Participle: This form is used in progressive tenses (present progressive, past progressive, future progressive) and to form participial phrases. Examples: *running*, *eating*, *sleeping*.
These four forms are essential for understanding and using verbs correctly in English.