Burden of proof; preponderant evidence

It is a basic rule in evidence that he who alleges must prove his case or claim by the degree of evidence required.
x x x Ei incumbit probatio qui dicit, non qui negat. [The Supreme] Court has consistently applied the ancient rule that "if the plaintiff, upon whom rests the burden of proving his cause of action, fails to show in a satisfactory manner the facts upon which he bases his claim, the defendant is under no obligation to prove his exception or defense."[1]
In civil cases, the quantum of proof required is preponderance of evidence, which connotes "that evidence that is of greater weight or is more convincing than that which is in opposition to it. It does not mean absolute truth; rather, it means that the testimony of one side is more believable than that of the other side, and that the probability of truth is on one side than on the other."[2]

[1] Martin v. Court of Appeals, G.R. No. 82248, January 30, 1992, 205 SCRA 591, 596, citing Belen v. Belen, 13 Phil. 202, 206 (1909).

[2] Reyes v. Century Canning Corporation, G.R. No. 165377, February 16, 2010, 612 SCRA 562, 570.