Definition
A Latin maxim meaning "each person skilled in their own art" or "to every person expert in his own craft." The principle holds that in matters requiring specialized knowledge or skill, a person who is recognized as an expert or master in a given trade, profession, or art is to be believed and relied upon with respect to questions within that domain. In legal contexts, the maxim has been invoked to justify deference to expert opinion and to support the competency of witnesses testifying about matters within their particular area of skill or expertise.
Common Confusion
This maxim is occasionally conflated with the distinct principle cuique in arte sua credendum est ("each person is to be believed in their own art"), which expresses substantially the same idea. The two phrases are functional equivalents in most historical legal usage and should not be treated as meaningfully different doctrines. Researchers encountering either form in historical sources can treat them as expressing the same underlying principle of expert deference.
Why It Matters in Research
This maxim belongs to a family of Latin legal principles that governed evidentiary weight and testimonial competence in common law courts before modern expert witness doctrine was codified. Researchers encountering this phrase in older opinions, pleadings, or treatises should understand it as a precursor to what is now addressed by rules governing expert testimony — Federal Rules of Evidence Rule 702 and its state equivalents in American jurisdictions, or similar provisions elsewhere.
The maxim appears infrequently in modern case law but surfaces with some regularity in historical English and early American decisions and in treatises on evidence and pleading. Its absence from everyday modern legal writing does not diminish its interpretive value when working with pre-twentieth-century sources. When a historical court invokes this phrase, it is typically doing one of two things: affirming that a craftsman or tradesman is competent to testify about practices within his trade, or establishing that a professional's judgment in their field carries presumptive authority.
Researchers should be alert to variant spellings. The term appears in historical sources with inconsistent orthography — "perito" is occasionally rendered "perjto" in older typeset editions, a compositor's artifact rather than a meaningful variant. Do not treat these as distinct phrases.
The source material available for this entry from Black's 2nd Edition appears to contain a misattributed entry — the text provided describes the cucking-stool or ducking-stool, a historical punishment device, and bears no relationship to this maxim. This is almost certainly a digitization or indexing error in the underlying source. Researchers relying on digitized versions of historical dictionaries should be aware that OCR errors and page-break misattributions can produce exactly this kind of phantom cross-contamination between adjacent or nearby entries. The definition of cuilibet in arte sua perito must be reconstructed from the maxim's established common law usage rather than from the corrupted Black's entry.
Historical Dictionary Support
Black's 2nd Edition, as available in the source material consulted, does not yield a usable entry for this term — the text attributed to it describes an entirely different subject (the cucking-stool). This is a known hazard with digitized legal reference works, where OCR processing and metadata errors can associate text blocks with incorrect headwords.
Broom's Legal Maxims, a standard historical authority on Latin legal principles, treats the broader category of expert deference maxims and provides context for understanding how English courts applied the principle that a person's craft-knowledge commands authority within its proper sphere. Older treatises on evidence, including those of Gilbert and Starkie, address the competency of tradesmen and artisans as witnesses in ways that reflect the underlying logic of this maxim, even where they do not quote it directly.
The maxim is part of a cluster of related Latin principles governing knowledge, expertise, and reliance — including the allied idea that ignorance of one's own trade is no excuse, and the broader principle that specialized knowledge creates both authority and responsibility.