Definition
A Latin adjective meaning "capable," "able," or "having capacity." In legal usage, *capax* appears almost exclusively as the first element of compound phrases that describe whether a person possesses the legal or mental capacity required to perform a specific act, bear legal responsibility, or hold a right. Standing alone, *capax* is a term of art signifying legal capacity in the abstract; its meaning is fully realized only in context through its compounds.
The two compounds of greatest historical importance are:
1. CAPAX DOLI — Capable of criminal intent; possessing the mental development to form a guilty mind (*mens rea*). A person who is *capax doli* can be held criminally responsible for a wrongful act. The opposite is *doli incapax* — incapable of crime — a presumption historically applied to children below a certain age.
2. CAPAX NEGOTII — Capable of transacting business; having the legal competence to enter into contracts, manage property, or otherwise conduct legal affairs. The phrase describes general civil capacity, as distinguished from criminal capacity under *capax doli*.
Common Confusion
*Capax* is often encountered in historical sources as shorthand for *capax doli*, which can mislead researchers who encounter the bare term and assume criminal incapacity is the only dimension at issue. The civil capacity sense (*capax negotii*) is equally established but appears less frequently in reported cases, making it easy to overlook when surveying older materials. Separately, *doli incapax* and *capax doli* are mirror-image phrases, and researchers should take care not to invert their meanings: *capax doli* affirms capacity; *doli incapax* negates it.
Why It Matters in Research
*Capax* functions as a gateway term in Law Mind's corpus. It rarely appears as a standalone index entry in primary legal materials; instead, researchers must trace it through its compounds. Any search strategy built around *capax* alone will miss the bulk of relevant doctrine, which is indexed under *doli incapax*, *capax doli*, *mens rea*, and *legal capacity*.
The doctrine of *doli incapax* is the most litigation-rich application. In English common law, children under seven were conclusively presumed *doli incapax*; children between seven and fourteen were presumptively incapable but the presumption could be rebutted. Historical cases and treatises will use *capax doli* and *doli incapax* interchangeably as positional opposites — the same doctrine described from both ends. Researchers working in nineteenth-century criminal law sources should expect both formulations.
For civil capacity research, *capax negotii* connects to a broader doctrinal cluster: infancy, coverture, mental incompetency, and guardianship. In equity materials especially, the question of whether a party was *capax negotii* determined whether a transaction could be ratified, voided, or enforced. The phrase appears in treatises on contract, trusts, and real property conveyances where capacity to act was contested.
Temporal trap: The age thresholds associated with *capax doli* shifted across jurisdictions and were modified by statute in many common law systems during the nineteenth and twentieth centuries. Historical sources reflect the common law age-based presumptions; modern sources may reflect statutory modification or abolition of the presumption. Do not assume continuity.
Historical Dictionary Support
Burrill and Anderson agree on the core meaning — *capax* signifies one who is able to receive, hold, or act — and both anchor the term's legal significance in its compounds. Burrill's definition is narrower, pointing primarily to the sense of "one who takes or holds" and referring readers directly to *doli capax* (his formulation of the phrase). Anderson is more systematic, explicitly distinguishing the criminal capacity compound (*capax doli*) from the civil capacity compound (*capax negotii*) and cross-referencing *dolus* for the fuller treatment of intent doctrine.
Neither dictionary provides extended analysis under *capax* itself; both treat it as a threshold cross-reference rather than a substantive entry. This accurately reflects how the term functions in legal literature: it does not carry independent doctrine but serves as the prefix through which capacity doctrine is organized. Researchers should treat both entries as pointers, not as complete accounts.
Jurisdictional Note
The *doli incapax* presumption and the age thresholds defining *capax doli* varied meaningfully between English common law, American jurisdictions, and civilian systems. Several common law jurisdictions have modified or abolished the presumption by statute. Civil capacity doctrine under *capax negotii* similarly reflects local rules on the age of majority, incompetency standards, and guardianship regimes.