Who's an Alternative Defendant?

Alternative defendants are those who may be joined as such in the alternative by the plaintiff who is uncertain from whom among them he is entitled to a relief, regardless of whether or not a right to a relief against one is inconsistent with that against the other. Where the plaintiff cannot definitely identify who among two or more persons should be impleaded as a defendant, he may join all of them as defendants in the alternative.
Under Sec. 13, Rule 3, "where the plaintiff is uncertain against who of several persons he is entitled to relief, he may join any or all of them as defendants in the alternative, although a right to relief against one may be inconsistent with a right of relief against the other." Since the rule allows a suit against defendants in the alternative, the rule also allows alternative causes of action (Sec. 2, Rule 8) and alternative defenses (Sec. 5[b], Rule 6).