Short answer. Section 3 of Rule 6 defines the complaint as the pleading alleging the plaintiff's cause or causes of action, and requires that the names and residences of both the plaintiff and the defendant be stated in it. Getting these basics right matters, since defects in identifying the parties can affect service of summons and venue.
What the law says
The complaint is the pleading alleging the plaintiff's or claiming party's cause or causes of action. The names and residences of the plaintiff and defendant must be stated in the complaint.
Rule 6, Section 3 — Complaint. Read the full provision →
What a complaint is for
Section 3 defines the complaint as the pleading in which the plaintiff (or claiming party) alleges their cause or causes of action. This is the document that formally initiates an ordinary civil action — it is where the plaintiff first sets out, in writing, the basis on which they are asking the court to grant them relief against the defendant. Everything that follows in the case, from the defendant's answer to the eventual judgment, responds to and is measured against what this initial pleading actually alleged.
The two mandatory identifying details
Beyond alleging the cause of action, Section 3 specifically requires that the complaint state the names and residences of the plaintiff and the defendant. This is not incidental information — identifying who exactly is suing and being sued, and where they reside, matters for questions like proper service of summons, venue, and simply ensuring the court and the opposing party know precisely who is involved in the litigation. A complaint that omits the plaintiff's or defendant's name or residence is not automatically fatal to the case, but it invites objection and possible correction before the litigation can proceed smoothly, since the clerk of court and the sheriff both rely on this information to properly issue and serve summons in the first place.
Multiple causes of action are contemplated
The definition's reference to a plaintiff's 'cause or causes of action' — plural — signals that a single complaint may allege more than one cause of action against the defendant, consistent with how civil actions are commonly structured when a plaintiff has several distinct legal grievances against the same party arising from related or separate transactions. A plaintiff who owes rent, a loan, and damages from a separate incident to the same defendant, for instance, need not file three complaints; the rules on joinder of causes of action let all of them be alleged together in one pleading, provided the other requirements for joinder — such as jurisdiction and venue over all the claims — are met.