How to identify identical cause of action
"Cause of action" is the act or omission by which a party violates the right of another.[1] 
The settled rule is that the identity of causes of action does not mean absolute identity. Otherwise, a party could easily escape the operation of res judicata by changing the form of the action or the relief sought.[2] The test to determine whether the causes of action are identical is to ascertain whether the same evidence will sustain both actions, or whether there is an identity of the facts essential to the maintenance of the two actions. If the same facts or evidence would sustain both, the two actions are considered the same, and a judgment in the first case would be a bar to the subsequent action. Hence, a party cannot, by varying the form of action or adopting a different method of presenting the case, escape the operation of the principle that one and the same cause of action shall not be twice litigated between the same parties or their privies.[3]
Among several tests resorted to in ascertaining whether two suits relate to a single or common cause of action are: (1) whether the same evidence would support and sustain both the first and the second causes of action; and (2) whether the defenses in one case may be used to substantiate the complaint in the other. Also fundamental is the test for determining whether the cause of action in the second case existed at the time of the filing of the first complaint.[4]
[1] RULES OF COURT, Rule 2, Sec. 2.
The settled rule is that the identity of causes of action does not mean absolute identity. Otherwise, a party could easily escape the operation of res judicata by changing the form of the action or the relief sought.[2] The test to determine whether the causes of action are identical is to ascertain whether the same evidence will sustain both actions, or whether there is an identity of the facts essential to the maintenance of the two actions. If the same facts or evidence would sustain both, the two actions are considered the same, and a judgment in the first case would be a bar to the subsequent action. Hence, a party cannot, by varying the form of action or adopting a different method of presenting the case, escape the operation of the principle that one and the same cause of action shall not be twice litigated between the same parties or their privies.[3]Among several tests resorted to in ascertaining whether two suits relate to a single or common cause of action are: (1) whether the same evidence would support and sustain both the first and the second causes of action; and (2) whether the defenses in one case may be used to substantiate the complaint in the other. Also fundamental is the test for determining whether the cause of action in the second case existed at the time of the filing of the first complaint.[4]
[1] RULES OF COURT, Rule 2, Sec. 2.
[2] Pilar Development Corp. v. Court of Appeals, G.R. No. 155943, 13 August 2013.
[3] Yap v. Chua, G.R. No. 186730, 13 June 2012, 672 SCRA 419.
[4] Supra.
