Definition
Ordinary skill refers to the level of competence, knowledge, and ability that a reasonably proficient practitioner in a given field or trade would be expected to possess and exercise. It is not the highest possible skill, nor mere rudimentary competence, but rather the middle standard — what someone familiar with and experienced in the relevant work would ordinarily bring to it.
The term operates across several distinct legal contexts:
1. TORT / CONTRACT LAW: The standard of care owed by professionals and tradespeople. A person who undertakes work in a professional or clearly defined capacity is bound to perform with the skill ordinarily possessed by competent practitioners in that field. Falling below this standard may constitute negligence or breach of contract.
2. PATENT LAW: "Ordinary skill in the art" (also rendered as "a person of ordinary skill in the art," abbreviated POSITA or PHOSITA) is the objective standard used to assess obviousness, claim construction, and enablement. It asks what a hypothetical skilled practitioner — not a genius, not a novice — in the relevant technical field would know and understand at the time of the invention.
These two contexts share a common conceptual core — an objective, mid-range competence standard — but apply it in very different procedural settings and with different legal consequences.
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Common Language
Modern common usage (Wiktionary): "Ordinary" means standard, usual, or not exceptional. "Skill" means proficiency or ability acquired through training or experience. Together, the phrase in common speech simply means average ability.
Historical common usage (Webster's 1913): "Ordinary" is defined as of common quality, not distinguished by superior excellence or inferiority. "Skill" is defined as familiar knowledge of any art or science united with readiness and dexterity in execution.
The gap between common and legal meaning is subtle but consequential. In everyday speech, "ordinary skill" might suggest mediocrity or bare adequacy. In law, it is a carefully constructed objective standard — neither the ceiling nor the floor of competence, but a normative benchmark against which conduct is measured. The standard is not self-effacing; in patent law especially, a person of ordinary skill in the art may possess substantial technical sophistication. Calling this "ordinary" reflects the field's baseline, not society's.
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Common Confusion
ORDINARY SKILL vs. REASONABLE CARE: In tort law, ordinary skill and reasonable care are closely related but not identical. Reasonable care is the general negligence standard applicable to all persons. Ordinary skill is the professional variant — it incorporates field-specific knowledge and is therefore a higher, more demanding benchmark when applied to specialists. A surgeon is not held merely to the standard of a reasonable layperson; she is held to the ordinary skill of a competent surgeon.
ORDINARY SKILL vs. BEST SKILL / HIGHEST SKILL: Courts and older treatises occasionally distinguish between contracting for ordinary skill and contracting for the highest or best skill. Engaging a specialist does not automatically guarantee the best possible outcome, only ordinarily skillful performance. This distinction matters in breach of contract claims.
PATENT LAW "ORDINARY SKILL IN THE ART" vs. TORT "ORDINARY SKILL": These share a name and a conceptual ancestor but are evaluated differently. In patent law, ordinary skill in the art is assessed at the time of the invention and is defined by factors such as the level of education common in the field, the nature of the problems addressed, and the sophistication of prior art solutions. In tort law, the standard is assessed at the time of the allegedly deficient conduct and tracks community practice and professional consensus.
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Why It Matters in Research
The term "ordinary skill" appears across legal history in two largely separate doctrinal streams — professional liability and patent law — and researchers must be alert to which stream their sources address.
In professional liability sources predating the twentieth century, ordinary skill is the workhorse standard for tradesmen, physicians, lawyers, and others holding themselves out for hire. Bouvier's treatment reflects this tradition directly: the standard is relational, asking what a person "conversant with the matter undertaken" might reasonably be supposed to know. This is a community-of-practice standard, and its content shifted as professions formalized, licensed, and diverged.
In patent law, the "person of ordinary skill in the art" standard crystallized through twentieth-century case development and was central to the Supreme Court's obviousness framework. Researchers working in patent doctrine will find that modern sources — regulations, claim construction briefs, expert declarations — are where this standard lives, not in the historical dictionaries. Bouvier's and its contemporaries have essentially nothing on the patent law application.
A trap for historical researchers: older sources frequently describe ordinary skill in ways that sound deferential to local custom or trade practice. Modern tort law has moved toward a more nationally or professionally standardized benchmark, particularly for licensed professions. What counted as "ordinary skill" in an 1850 physician is not what courts assess today. Do not import historical descriptions of skill standards into modern negligence analysis without accounting for this evolution.
Jurisdictional variation in tort law matters: some states define the professional negligence standard by reference to the same or similar locality (the "locality rule"), while others apply a national standard. This affects what "ordinary" means in practice and how expert witnesses frame their testimony.
For patent law researchers, the level of ordinary skill in the art is a factual determination made record-by-record. Secondary sources and treatises can explain the framework, but the content of the standard for any specific patent must be established from the prosecution history, expert testimony, and the technical field's prior art landscape.
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Historical Dictionary Support
Bouvier's Law Dictionary defines ordinary skill as "such skill as a person conversant with the matter undertaken might be reasonably supposed to have." The definition is functional and relational: it is not an abstract threshold but one derived from the community of practitioners in the relevant field. Bouvier cross-references NEGLIGENCE and Cooley on Torts, signaling that ordinary skill is primarily understood as a negligence standard — deviation from it being one route to liability.
The string of case citations Bouvier supplies spans multiple jurisdictions and decades, reflecting that this was well-established common law doctrine by the mid-nineteenth century, not a statutory creation. This breadth is useful: it confirms that ordinary skill as a professional liability standard was not jurisdiction-specific at the doctrinal level, even if its content varied locally.
What Bouvier's and comparable historical dictionaries miss entirely is the patent law application. The "person of ordinary skill in the art" as an obviousness and claim-construction standard is a creature of later doctrine. Researchers should not expect historical legal dictionaries to illuminate this usage; modern patent treatises and regulatory materials are the appropriate sources.
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Jurisdictional Note
In professional negligence, most U.S. jurisdictions have abandoned the historical "locality rule" (which measured ordinary skill against local practitioners only) in favor of a national or specialty-based standard, particularly for licensed professionals. Some jurisdictions retain modified locality rules for general practitioners in underserved areas. In patent law, ordinary skill in the art is a federal standard applied uniformly, though its factual content varies by technology and case record.
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