What is the test for a plaintiff who cannot prove that he could have collected the full amount of the underlying judgment but only a portion thereof?

We have alluded to cases where a plaintiff could not prove that he could have collected the full amount of the underlying judgment but only a portion thereof. His damages in the malpractice action are then limited to that portion of the underlying judgment he could have collected. This is consistent with the fundamental principle of tort law that a plaintiff claiming negligence must prove causation. As in other negligence actions, an attorney who fails to exercise due care in the handling of a client's affairs is liable "for all damages directly and proximately caused by his negligence." (Pete v. Henderson (1954) 124 Cal.App.2d 487, 489, 269 P.2d 78.) The attorney's negligence causes the plaintiff to lose only that portion of the underlying judgment that could have been collected.

In McDow v. Dixon (1976) 138 Ga.App. 338, 226 S.E.2d 145, the Georgia court repeated the common refrain that a malpractice plaintiff must prove solvency of the debtor. However, the court explained that this requirement "`is simply an application of the doctrine, everywhere recognized, that a party claiming damages must prove not only the wrong, but the amount of his damages as well'" (Id. at p. 147.) The court continued: "A client suing his attorney for malpractice not only must prove that his claim was valid and would have resulted in a judgment in his favor, but also that said judgment would have been collectible in some amount, for therein lies the measure

[99 Cal.App.4th 572]