Unlawful detainer is an action to recover possession of real property from one who illegally withholds possession after the expiration or termination of his right to hold possession under any contract, express or implied. The possession by the defendant in unlawful detainer is originally legal but became illegal due to the expiration or termination of the right to possess. The proceeding is summary in nature, jurisdiction over which lies with the proper MTC or metropolitan trial court. The action must be brought up within one year from the date of last demand, and the issue in the case must be the right to physical possession. Firm is the rule that as long as these allegations demonstrate a cause of action for unlawful detainer, the court acquires jurisdiction over the subject matter. The requirement that the complaint should aver, as jurisdictional facts, when and how entry into the property was made by the defendants applies only when the issue is the timeliness of the filing of the complaint before the MTC, and not when the jurisdiction of the MTC is assailed because the case is one for accion publiciana cognizable by the RTC. This is because, in forcible entry cases, the prescriptive period is counted from the date of defendants’ actual entry into the property; whereas, in unlawful detainer cases, it is counted from the date of the last demand to vacate. Hence, to determine whether the case was filed on time, there is a necessity to ascertain whether the complaint is one for forcible entry or for unlawful detainer; and since the main distinction between the two actions is when and how defendant entered the property, the determinative facts should be alleged in the complaint.