The defendant lawyer may deny that he/she was negligent, or deny that any negligence caused damage, or both. Regarding negligence, the defendant lawyer might simply deny that there were acts or omissions falling below the standard of care, or claim that any mistakes were somebody else’s fault, including another lawyer or the client. Regarding damages, the defendant lawyer might argue that the plaintiff’s position in the underlying case was untenable, and he/she would not have prevailed. The factual and legal arguments in support of these defenses are potential infinite, reflecting the wide diversity of circumstances presented in each case.
There are, however, certain specific arguments commonly raised by the defense in legal malpractice cases. One significant defense is sometimes referred to as the "attorney judgment" rule. In Washington, under this rule, an attorney cannot be liable for making an allegedly erroneous decision involving honest, good faith judgment if (1) that decision was within the range of reasonable alternatives from the perspective of a reasonable, careful and prudent attorney in Washington; and (2) in making that judgment decision the attorney exercised reasonable care. Clark County Fire District v Bullivant Houser Bailey P.C., 180 Wash.App.689, 706, 324 P.3d 743, 752 (2014).
In general, errors in judgment or in trial tactics do not subject an attorney to liability for legal malpractice. Halvorsen v. Ferguson, 46 Wn.App. 708, 717, 735 P.2d 675 (1986), including and particularly when the error involves an uncertain, unsettled, or debatable proposition of law. However, an attorney's immunity from judgmental liability is conditioned upon reasonable research undertaken to ascertain relevant legal principles and to make an informed judgment.
Oregon has not expressly adopted an "attorney judgment rule" as such, but other rules to determine attorney negligence create similar challenge in attempting to prove negligence when the alleged acts and omissions involve discretionary tactical decisions in which the lawyer’s decision was among a reasonable range of alternatives.
The defense in a legal malpractice case frequently attempts to shoehorn much of all of the lawyer’s alleged mistakes into this category of discretionary judgment, and to argue that a special rule of immunity applies. In reality, it still boils down to the question whether the lawyer was negligent. The fact that, in retrospect, there might have been better courses of action, does not necessarily mean the course chosen was negligent. There is no bright line to determine such questions, but certain kinds of attorney mistakes can present more challenges for a plaintiff than others.