Traditionally, there were only two defenses to negligence: contributory negligence and assumption of risk. Both constituted complete defenses and completely barred the plaintiff from recovery. In all but a handful of states, contributory negligence has been converted by statute or judicial ruling into comparative negligence. Unlike contributory negligence, comparative negligence need not be a complete bar to the plaintiff's recovery, but acts only as partial bar resulting in a percentage deduction from otherwise recoverable damages.
Contributory negligence is “conduct on the part of the plaintiff which falls below the standard of conduct to which he should conform for his own protection, and which is a legally contributing cause . . . in bringing about the plaintiff's harm.” (Restatement § 463.]
Contributory negligence is a complete defense to negligence.
[B] Last Clear Chance Doctrine
The last clear chance doctrine instructs the court to ignore the plaintiff's contributory negligence if the defendant's negligence occurred after the plaintiff's contributory negligence. See Davies v. Mann, 10 M&W 546, 152 Eng. Rep. 588 (1842).
Most jurisdictions reject the last clear chance doctrine when replacing contributory negligence with comparative negligence.
In almost all states, contributory negligence has been replaced by some form of comparative negligence, often called comparative fault. [See Restatement (Third) of Torts, Apportionment of Liability § 7, endorsing comparative negligence.]
Under comparative negligence, “the conduct on the part of the plaintiff which falls below the standard of conduct which he should conform to for his own protection and which is a legally contributing cause . . . in bringing about the plaintiff's harm” is only a partial bar to the plaintiff's recovery. Comparative negligence reduces the plaintiff's recovery by the percentage of responsibility for the injury attributable to the plaintiff.
[A] Pure Comparative Negligence
Under pure comparative negligence plaintiffs can recover some percentage from liable defendants regardless of the extent of their own negligence. [See, e.g., Li v. Yellow Cab Co., 532 P.2d 1226 (Cal. 1975).]
[B] Modified Comparative Negligence
Under the modified system, plaintiffs are allowed a partial recovery just as in pure comparative negligence until the plaintiff is either more negligent (greater than 50% at fault) than the defendant(s) or in other states equal to the negligence of the defendant(s).
Along with contributory negligence, assumption of risk has traditionally existed as a complete defense to negligence.
There are thus three basic elements to the assumption of risk. The plaintiff must (1) know a particular risk and (2) voluntarily (3) assume it. [See Restatement § 496C; see also, e.g., Murphy v. Steeplechase Amusement Co., Inc., 166 N.E. 173 (N.Y. 1929).]
[B] Classifications of Assumption of Risk
 Express Versus Implied Assumption of Risk
Assumption of risk is generally divided into two types: express and implied. Express assumption of risk exists when, by contract or otherwise, a plaintiff explicitly agrees to accept a risk. [See Restatement § 496B.] Implied assumption of risk exists when the plaintiff's voluntary exposure to risk is derived merely from her behavior, and not from explicit assent. [See Restatement § 496C.]
 Express Assumption of Risk
If an assumption of risk is characterized as express, it can be invalidated if it is found contrary to public policy. Conversely, courts are likely to uphold express assumption of risk when the plaintiff's participation is clearly voluntary, such as the decision to engage in risky recreational pursuits. [See Restatement § 496B; see also, e.g., Woodall v. Wayne Steffner Productions, Inc., 20 Cal. Rptr. 572 (Cal. Ct. App. 1962).]
 Implied Assumption of Risk
The modern trend is to allow implied assumption of risk to be absorbed into comparative negligence. This allows the jury to treat assumption of risk as a partial defense. [See, e.g., Knight v. Jewett, 834 P.2d 696 (Cal. 1992).]
An immunity protects a defendant from tort liability. Unlike a defense, it is not dependent on the plaintiff's behavior, but on the defendant's status or relationship to the plaintiff.
[B] Charitable Immunity
Historically, charitable organizations were immune from tort liability. Increasingly, this immunity has been abrogated. [See Restatement § 895E.]
[C] Spousal Immunity
Historically, spouses could not sue each other. The majority of states have eliminated spousal immunity. [See, e.g., Klein v. Klein, 376 P.2d 70 (Ca. 1962); Restatement § 895F.]
[D] Parent-Child Immunity
Parent-child immunity precludes tort actions between parents and their non-adult children. [See Small v. Morrison, 118 S.E. 12, 16 (N.C. 1923).] Unlike spousal immunity, which has been eliminated in most states, parent-child immunity still exists in some form in many jurisdictions. [See, e.g., Gibson v. Gibson, 479 P.2d 648 (Cal. 1971).]
[E] Governmental Immunity
Governmental immunity protects the government from tort liability. Under the common law, the immunities were complete and prevented any tort suits against the government.
Many states and the federal government have passed detailed statutes modifying the immunities in specific instances. One general provision normally included allows immunity for discretionary functions but not ministerial acts. Discretionary functions are policy-making decisions. Ministerial acts constitute government conduct which implements or executes policy decisions. [See, e.g., Tarasoff v. Regents of the University of California, 551 P.2d 334 (Cal. 1976).]