Study guide
15.6 Breach of Duty & Res Ipsa Loquitur
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1 Introduction & FYLSE Examination Guide
1.1 FYLSE Exam Structure, Passing Standard & Administration 1.2 Study Method, Pacing & MBE-Style Technique
2 Contracts: Mutual Assent, Capacity & Contract Formation
2.1 The Offer & Objective Theory of Assent 2.2 Termination & Irrevocability of Offers 2.3 Acceptance & the Mailbox Rule 2.4 Mirror Image Rule & UCC 2-207 Battle of the Forms 2.5 Mistake in Contract Formation 2.6 Fraud, Duress, Undue Influence & Illegality 2.7 Capacity to Contract
3 Contracts: Consideration, Estoppel & Implied Obligations
3.1 Consideration & the Bargained-For Exchange 3.2 Past & Moral Consideration, Pre-Existing Duty & Modification 3.3 Promissory Estoppel & Detrimental Reliance 3.4 Implied-in-Fact Contracts & Quasi-Contract 3.5 Implied Covenant of Good Faith, Fair Dealing & Indefinite Terms
4 Contracts: Third-Party Beneficiaries, Assignment & Delegation
4.1 Third-Party Beneficiary Contracts 4.2 Assignment of Rights 4.3 Delegation of Duties
5 Contracts: Statute of Frauds, Parol Evidence & Interpretation
5.1 Statute of Frauds: Contracts Within the Statute 5.2 Satisfying the Statute: Writing, Signature & Exceptions 5.3 The Parol Evidence Rule 5.4 Contract Interpretation & Canons of Construction
6 Contracts: Performance, Conditions, UCC Warranties & Breach
6.1 Conditions: Express, Constructive & Excuse 6.2 Substantial Performance vs. Perfect Tender 6.3 Cure, Rejection, Revocation & Installment Contracts 6.4 UCC Article 2 Warranties & Risk of Loss 6.5 Anticipatory Repudiation & Insecurity
7 Contracts: Remedies, Discharge & Changed Circumstances
7.1 Expectation Damages & Their Limitations 7.2 Reliance, Restitution & Liquidated Damages 7.3 Specific Performance & Injunctive Relief 7.4 UCC Article 2 Buyer's and Seller's Remedies 7.5 Impossibility, Impracticability & Frustration of Purpose 7.6 Discharge by Agreement: Rescission, Novation & Accord and Satisfaction
8 Criminal Law: Principles of Criminal Liability & Mens Rea
8.1 Actus Reus, Voluntary Acts & Omissions 8.2 Criminal Causation & Intervening Causes 8.3 Common Law & Model Penal Code Mens Rea 8.4 Mistake of Fact, Mistake of Law & Concurrence
9 Criminal Law: Inchoate Offenses & Accomplice Liability
9.1 Criminal Attempt & Impossibility 9.2 Solicitation & the Merger Doctrine 9.3 Conspiracy & Merger Doctrine 9.4 Accomplice Liability: Actus Reus & Mens Rea 9.5 Scope of Accomplice Liability, Withdrawal & Parties to Crime
10 Criminal Law: Homicide & Crimes Against the Person
10.1 Common Law Murder & Malice Aforethought 10.2 Degrees of Murder, Premeditation & Deliberation 10.3 The Felony Murder Rule & Its Limitations 10.4 Voluntary & Involuntary Manslaughter 10.5 Non-Homicide Crimes Against the Person
11 Criminal Law: Property Crimes, Theft & Habitation
11.1 Common Law Larceny 11.2 Embezzlement & False Pretenses 11.3 Robbery & Extortion 11.4 Receiving Stolen Property 11.5 Burglary 11.6 Arson
12 Criminal Law: Defenses: Capacity, Justification & Excuse
12.1 Insanity: The Four Legal Tests 12.2 Intoxication, Diminished Capacity & Infancy 12.3 Self-Defense & Defense of Others 12.4 Defense of Property, Habitation & Law Enforcement Privileges 12.5 Duress & Necessity 12.6 Entrapment & Mistake as an Excuse
13 Torts: Intentional Torts to Persons & Property
13.1 Intent, Motive & Incapacity in Intentional Torts 13.2 Transferred Intent 13.3 Battery & Assault 13.4 False Imprisonment 13.5 Trespass to Land 13.6 Trespass to Chattels & Conversion
14 Torts: Privileges & Defenses to Intentional Torts
14.1 Consent: Express, Implied & Capacity 14.2 Exceeding & Vitiating Consent 14.3 Self-Defense & Defense of Others (Tort) 14.4 Defense of Property & Recapture of Chattels 14.5 Public & Private Necessity 14.6 The Shopkeeper's Privilege
15 Torts: Negligence — Duty of Care & Breach
15.1 Duty of Care & the Foreseeable Plaintiff 15.2 Affirmative Duties to Act & Special Relationships 15.3 Standard of Care: The Reasonable Person & Children 15.4 Professional Negligence, Informed Consent & Negligence Per Se 15.5 Land Possessor Liability & Premises Duties 15.6 Breach of Duty & Res Ipsa Loquitur
16 Torts: Causation, Defenses, Multiple Tortfeasors, Wrongful Death & Damages
16.1 Cause in Fact & Multiple Actors 16.2 Proximate Cause & Intervening Forces 16.3 Contributory, Comparative Negligence & Assumption of Risk 16.4 Joint and Several Liability, Contribution & Indemnity 16.5 Vicarious Liability & Non-Delegable Duties 16.6 Wrongful Death & Survival Actions 16.7 Statute of Limitations & Claim Accrual 16.8 Tort Damages: Compensatory, Nominal, Punitive & Mitigation
17 Torts: Strict Liability & Products Liability
17.1 Strict Liability for Animals 17.2 Abnormally Dangerous Activities & Scope of Risk 17.3 Strict Products Liability & Defect Categories 17.4 Products Liability Under Negligence, Warranty & Misrepresentation 17.5 Defenses to Products Liability
18 Torts: Emotional Distress, Defamation, Privacy & Economic Torts
18.1 Intentional Infliction of Emotional Distress 18.2 Negligent Infliction of Emotional Distress 18.3 Common Law Defamation: Elements, Libel & Slander 18.4 Constitutional Limits, Privileges & Defenses to Defamation 18.5 Invasion of Privacy 18.6 Nuisance & Economic Torts
15.6 Breach of Duty & Res Ipsa Loquitur
Key Takeaways Explain This Topic AI
Breach occurs when an actor's conduct falls below the applicable standard of care, evaluated under the Learned Hand formula (B < P x L) where liability attaches if the burden of precautions is less than the probability multiplied by the gravity of foreseeable harm.
Evidence of industry custom or trade practice is admissible to show reasonableness, but under The T.J. Hooper, compliance with custom is not conclusive proof of due care because an entire industry may be negligent.
Res ipsa loquitur permits a circumstantial inference of negligence where the event ordinarily does not happen absent negligence, the instrumentality was within the defendant's exclusive control, and the plaintiff was free from contributing fault.
Procedurally, res ipsa loquitur creates a permissive inference that defeats a defendant's motion for a directed verdict or nonsuit; it does not shift the ultimate burden of proof or mandate a directed verdict for the plaintiff.
Under California's landmark Ybarra v. Spangard exception, an unconscious surgical patient who suffers unusual trauma during medical care can invoke res ipsa loquitur against all participating operating room personnel, shifting the burden of explanation to each defendant.
Last updated: September 2026
Breach of Duty & Res Ipsa Loquitur
Exam Snapshot: Proving breach of duty is the central battleground of negligence litigation. Once the governing standard of care is established, the plaintiff must introduce sufficient evidence to prove that the defendant's conduct failed to conform to that standard. Examinees must master two primary analytical frameworks: the economic balancing test of the Learned Hand Formula ( B < P × L B < P \times L B < P × L ) and the circumstantial evidentiary doctrine of Res Ipsa Loquitur ("the thing speaks for itself"). A critical FYLSE distinction is the exact procedural consequence of res ipsa loquitur: it creates a permissive inference that allows the case to reach the jury, not a mandatory presumption.
1. Defining Breach: The Learned Hand Cost-Benefit Calculus
Breach is the objective failure of an actor to conform their conduct to the required standard of care. When determining whether an actor's conduct created an unreasonable risk of harm, modern American jurisprudence applies the cost-benefit framework articulated by Judge Learned Hand in United States v. Carroll Towing Co. (2d Cir. 1947).
The Algebraic Formula: B < P × L B < P \times L B < P × L
In Carroll Towing , a barge broke away from a busy harbor pier because the bargee was absent for twenty-one hours, colliding with other vessels and sinking. Judge Hand defined the owner's duty to provide against resulting injuries as a function of three variables: Breach Exists If: B < P × L \text{Breach Exists If: } B < P \times L Breach Exists If: B < P × L
Variable Legal Meaning & Analytical Valuation
B B B Burden of Precaution: The financial cost, physical effort, practical inconvenience, and social utility forgone in adopting effective safety precautions to prevent the harm.
P P P Probability of Harm: The foreseeable statistical likelihood or probability that an accident will occur if precautions are omitted.
L L L Gravity / Magnitude of Loss: The severity, gravity, or magnitude of the resulting foreseeable personal injury or property damage if the risk materializes. Learned Hand Calculus Application
- ├── B < (P × L) ──▶ Burden is LESS than expected loss ──▶ CONDUCT IS UNREASONABLE (Breach of Duty)
- └── B ≥ (P × L) ──▶ Burden is GREATER than expected loss ──▶ CONDUCT IS REASONABLE (No Breach)
Marginal Risk Analysis: The formula is applied marginally. The question is not whether the overall activity has social value, but whether the marginal cost of taking an additional, specific precaution is outweighed by the marginal reduction in foreseeable risk.
Social Utility: If an activity provides immense social utility (such as driving an emergency ambulance with sirens blaring, or maintaining electricity distribution during a storm), the social burden ( B B B ) of ceasing the activity is immense, justifying risks that would be negligent for a private commercial actor.
2. Industry Custom and Trade Practice: The T.J. Hooper Rule
In non-professional negligence cases, parties frequently introduce evidence of prevailing trade practices, industrial safety customs, or community usage to demonstrate whether conduct was reasonable.
Admissible, But Never Conclusive
Under the landmark ruling of Judge Learned Hand in The T.J. Hooper (2d Cir. 1932), industry custom is admissible as evidence of reasonable care, but it is NOT conclusive on the issue of negligence :
The Facts of The T.J. Hooper: Two commercial tugboats lost their coal-laden barges in an unexpected coastal storm. The tugs lacked working radio receivers that would have warned of the gale. At trial, the tug owners proved that the vast majority of commercial coastal tugboats did not carry radio receivers, asserting compliance with industry custom as a complete defense.
The Holding: Judge Hand rejected the defense, declaring that while custom is persuasive evidence, an entire industry may be negligent . A whole calling may unduly lag behind the adoption of relatively inexpensive, highly effective safety devices. The law fixes the standard of due care, not the self-interested customs of an industry. Evidentiary Role of Custom
├── Ordinary Negligence (The T.J. Hooper) ──▶ Custom is ADMISSIBLE, but NOT CONCLUSIVE (Jury decides due care)
└── Professional Malpractice (Doctors/Lawyers) ──▶ Custom DEFINES the legal standard of care as a MATTER OF LAW
FYLSE Distinction Alert: Keep the distinction between ordinary negligence and professional malpractice crystal clear. In medical or legal malpractice, conforming to established professional custom is a complete defense as a matter of law. In ordinary industrial or vehicular negligence, conforming to industry custom is merely an argument for the jury; the jury remains free to conclude that the entire industry custom is negligent.
3. Res Ipsa Loquitur ("The Thing Speaks for Itself")
In many accidents, the plaintiff cannot point to specific eyewitness testimony or direct mechanical proof showing exactly what the defendant did wrong. To prevent injustice when the circumstantial facts scream negligence, English common law developed the doctrine of Res Ipsa Loquitur ( Byrne v. Boadle , Exch. 1863 — a barrel of flour rolled out of a warehouse upper-story window and struck a pedestrian walking down the public street below).
The Three Classical Elements ( Restatement (Second) of Torts § 328D )
To invoke res ipsa loquitur, the plaintiff must establish three mandatory elements by a preponderance of the evidence: [ Rare Occurrence Absent Negligence ] + [ Exclusive Control by Defendant ] + [ Plaintiff Free from Fault ] = Res Ipsa Loquitur
Ordinarily Does Not Occur Absent Negligence: The accident or injury is of a kind that does not ordinarily happen unless someone was negligent. Common examples include commercial airplane crashes, surgical instruments left inside patients, elevators in free fall, and barrels falling from second-story warehouse windows.
Instrumentality Within Defendant's Exclusive Control: The instrumentality or agency that caused the injury was within the exclusive control of the defendant (or within the scope of the defendant's legal responsibility). This element eliminates the likelihood that a third party was the responsible actor.
Modern Flexibility: Modern courts do not require rigid physical custody at the microsecond of injury; it is sufficient that the evidence reasonably eliminates other external causes.
Plaintiff Free From Contributory Fault: The injury was not due to any voluntary action, contribution, or fault on the part of the plaintiff.
4. The Procedural Effect of Res Ipsa Loquitur
The single most heavily tested procedural aspect of torts on the FYLSE is the exact legal consequence of establishing res ipsa loquitur: Plaintiff Establishes Res Ipsa Loquitur Elements
- ├── Survives Defendant's Motion for Directed Verdict / Nonsuit ──▶ YES (Case must proceed to jury)
- ├── Shifts the Ultimate Burden of Proof to Defendant ──▶ NO (Burden remains with plaintiff)
- ├── Mandates a Directed Verdict in Favor of Plaintiff ──▶ NO (Jury may accept or reject inference)
- └── Effect: PERMISSIVE INFERENCE OF NEGLIGENCE ──▶ Jury is PERMITTED, but not required, to infer breach
- The Permissive Inference Rule (Majority)
In the overwhelming majority of American jurisdictions, res ipsa loquitur creates a permissive inference of negligence , not a rebuttable presumption:
Defeats Directed Verdict: Res ipsa loquitur satisfies the plaintiff's burden of production on duty and breach, ensuring the plaintiff survives a motion for nonsuit or directed verdict brought by the defendant.
Jury Discretion: The jury is permitted to infer that the defendant was negligent, but the jury is never legally required to do so. The jury may weigh the circumstantial evidence and find for the defendant.
Plaintiff Never Wins on Directed Verdict: Because the inference is merely permissive, the plaintiff is almost never entitled to a directed verdict on a res ipsa loquitur theory (unless the plaintiff's circumstantial proof is so overwhelmingly undisputed that no reasonable jury could find for the defendant).
5. The Multi-Defendant Medical Exception: Ybarra v. Spangard (1944)
Under strict traditional res ipsa loquitur rules, an injured plaintiff could not invoke the doctrine against multiple defendants if the plaintiff could not prove which specific defendant exercised exclusive control over the injury-causing instrumentality.
The Landmark California Ruling
In Ybarra v. Spangard (Cal. 1944), the California Supreme Court created a historic exception to prevent a medical "conspiracy of silence":
The Facts: An unconscious patient undergoing an appendectomy under general anesthesia was positioned on an operating table by several doctors and nurses. Following surgery, the patient developed severe pain and traumatic atrophy in his right shoulder, an area entirely unrelated to the abdominal appendectomy incision.
The Issue: The plaintiff could not pinpoint whether the surgeon, the anesthesiologist, or a particular surgical nurse mishandled his body or used a defective instrument.
The Rule of Law: Where a patient receives unusual, traumatic personal injuries while unconscious and in the course of medical treatment , all doctors and nurses who had any control over the patient's body or the surgical instrumentalities may be joined as defendants under res ipsa loquitur . The burden shifts to each defendant to explain their conduct and exculpate themselves .
Doctrinal Impact: Ybarra is a signature California tort doctrine. On the FYLSE, look for an unconscious surgical patient suffering unusual physical injuries outside the surgical field during an operation involving multiple medical personnel.
6. Master Evidentiary Matrix: Proving Breach
Evidentiary Doctrine Definition & Core Standard Primary Doctrinal Source Procedural Consequence at Trial
Learned Hand Calculus Breach if B < P × L B < P \times L B < P × L (Burden < Probability × \times × Loss). United States v. Carroll Towing Co. Submits economic balancing of reasonableness to jury.
Industry Custom Admissible evidence of trade practice; not conclusive. The T.J. Hooper Jury may find an entire industry's custom negligent.
Negligence Per Se Safety statute defines standard (Class of person / type of harm). Tedla v. Ellman ; Cal. Evid. Code § 669 Conclusive proof of duty/breach (or rebuttable presumption).
Res Ipsa Loquitur Circumstantial inference: exclusive control, rare without fault. Byrne v. Boadle ; Restatement § 328D Permissive inference ; defeats defendant's directed verdict.
Ybarra Medical Res Ipsa Unconscious patient; multiple surgical personnel joined. Ybarra v. Spangard Permissive inference against all personnel; shifts explanation burden.
- 7. Practical Exam Hypotheticals & FYLSE Traps
- Trap Scenario 6: The Directed Verdict Trap in Res Ipsa
Hypothetical: Patricia is walking past a five-story brick commercial bakery owned and operated by Dan when a twenty-pound sack of whole wheat flour falls from an open fourth-story window, striking Patricia on the shoulder. Patricia sues Dan in negligence. At trial, Patricia proves that the bakery was in Dan's exclusive possession, that sacks of flour do not fall out of bakery windows absent negligence, and that Patricia did nothing to cause the sack to fall. Patricia rests her case. Both Patricia and Dan move for directed verdicts.
Analysis: Dan's motion for a directed verdict will be denied because Patricia established the elements of res ipsa loquitur, creating a sufficient circumstantial inference of negligence to reach the jury. However, Patricia's motion for a directed verdict will also be denied . Res ipsa loquitur creates a permissive inference , not a mandatory legal presumption. The jury is entitled to reject the inference and find that an unexpected gust of wind or an unknown third-party intruder was responsible. The case must be submitted to the jury.