The four principal parts of every verb are:
- Base Form (or the infinitive without "to") – e.g., "walk"
- Past Simple – e.g., "walked"
- Past Participle – e.g., "walked" (used with auxiliary verbs)
- Present Participle – e.g., "walking" (used for continuous tenses)
These parts are essential for conjugating verbs in various tenses.