What is the function of a complaint?

The pleading alleging the plaintiff’s cause/s of action is called a "complaint." (Section 3, Rule 6) Its functions are:
  1. To inform the defendant clearly and definitely of the claims made against him so that he may be prepared to meet the issues at trial;
  2. To inform the defendant of all material facts on which the plaintiff relies to support his demand;
  3. To state the theory of a cause of action which forms the bases of plaintiff’s claim of liability (Tantuico v. Republic, G.R. No. 89114, 1991); and
  4. To assist the court in deciding the case, especially via the facts alleged and the reliefs prayed for.
A complaint is defined as a concise statement of the ultimate facts constituting the plaintiff's cause or causes of action.[1] Like all other pleadings allowed by the Rules of Court,[2] the complaint shall contain in a methodical and logical form a plain, concise and direct statement of the ultimate facts on which the plaintiff relies for his claim, omitting the statement of mere evidentiary facts.[3] Its office, purpose or function is to inform the defendant clearly and definitely of the claims made against him so that he may be prepared to meet the issues at the trial. The complaint should inform the defendant of all the material facts on which the plaintiff relies to support his demand; it should state the theory of a cause of action which forms the bases of the plaintiff's claim of liability.[4]

[1] Rules of Court, Rule 6, Sec. 3.
[2] Rules of Court, Rule 6, Sec. 2.
[3] Rules of Court, Rule 8, Sec. 1.
[4] Martin, Notes & Comments, Rules of Court, Vol. 1, 1986 ed., p. 279, citing 71 c.d.s., Sec. 63(b), p. 19.