Positive Perfective Form

The positive perfective form expresses an action or state that has been perfected, so the form can express a past event when used at the end of a sentence.

• Group 1: Change the final る to た
• Group 2: When the final syllable is
  
  く, change it to いた
  ぐ, change it to いだ
  す, change it to した
  む, ぬ, or ぶ, change it to んだ
  つ, る, or う, change it to った
  Exception: いく (to go) →いった
• Group 3: くる→きた、する→した

This form is a plain form rather than a polite form. So, when this form is used at the end of a sentence, it indicates that the speaker and the addressee are in a close relation (such as friends or family members). If this form is used at the end of a sentence in a piece of writing, it indicates that the style of the writing is impersonal (such as in essays and articles, as opposed to personal letters).