In regular verbs it is the same as the past tense form and is made by adding -ed to the verb stem (or just -d if the verb ends with the letter -e). In Irregular verbs it is formed in different ways.
The past participle is used to form a number of tenses:
 Present Perfect: I have smiled.
 Past Perfect: I had smiled.
 Future Perfect: I shall have smiled.
It is also used to form past tense with Modal Auxiliaries (I might have smiled, I should have smiled, etc.).
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