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Ken has cooked the dinner. 

Chris has written a letter to his mother. 

The first three participles in the examples above are the same as the ordinary past tense but ‘has’ or ‘had’ have been added. These are regular verbs and the past participle ends in ‘-ed’. In the last example ‘written’ is different and can only be used with the verb ‘to have’. A number of verbs are irregular, including the following: 

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When the verb ‘to have’ is added to the past participle, the finite verb is either the present perfect or the past perfect tense. This depends on which tense of the verb ‘to have’ has been used. 

