Definition
In legal usage, "arbitrary" describes a decision, action, or exercise of power that lacks adequate reason, principled basis, or fair justification. A determination is arbitrary when it is not supported by fair, solid, and substantial cause — when it rests on the decision-maker's will, caprice, or preference rather than on law, evidence, or reasoned judgment.
The term operates in two overlapping but distinct legal contexts:
1. ADMINISTRATIVE AND JUDICIAL REVIEW: A governmental or administrative action is arbitrary when it departs from rational basis — when no reasonable explanation connects the facts to the outcome, or when the decision-maker failed to consider relevant factors, relied on impermissible ones, or reached a conclusion that simply cannot be defended on the record. Under the federal Administrative Procedure Act, courts may set aside agency action found to be "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law." This is one of the most litigated standards in administrative law.
2. ARBITRARY PUNISHMENT OR PENALTY: A punishment is arbitrary when it is not fixed or defined by law, leaving the sentencing authority unconstrained by statutory standards or procedural limits. The Eighth Amendment's prohibition on cruel and unusual punishment, as interpreted through cases addressing the death penalty's application, targets arbitrariness in this sense — outcomes that vary by race, geography, or chance rather than by principled distinctions.
Common Language
Modern common usage (Wiktionary): Based on individual discretion or judgment; not based on any objective distinction, perhaps made at random; determined by impulse rather than reason, often connoting heavy-handedness.
Historical common usage (Webster's 1913): Depending on will or discretion; not governed by any fixed rules; exercised according to one's own will or caprice, conveying a notion of tendency to abuse the possession of power.
The gap between common and legal meaning is narrower here than for most legal terms, but it matters at the margins. In ordinary speech, "arbitrary" often implies mere randomness or personal whim. In law, the term is a term of art in review standards: a decision can be arbitrary even when the decision-maker had clear reasons, if those reasons do not hold up to scrutiny or are legally impermissible. Conversely, a decision that looks idiosyncratic may survive legal challenge if it is rationally connected to a legitimate purpose. The legal question is not whether the decision seems odd, but whether it is supported by fair and substantial cause.
Common Confusion
Arbitrary vs. Capricious: Courts and statutes often pair these terms — "arbitrary and capricious" — which can suggest they are synonyms. Historically, "arbitrary" emphasized absence of supporting reason, while "capricious" emphasized inconsistency or whim. In modern administrative law usage the two are largely treated as a single standard, but in some contexts courts distinguish them: an action is arbitrary when it lacks rational basis on the record; it is capricious when it reflects a sudden or erratic change in policy without explanation.
Arbitrary vs. Discretionary: Anderson's Dictionary of Law notes that "arbitrary" can mean "discretionary," and the overlap is real — both describe situations not governed by fixed rules. The distinction is normative: discretion, properly exercised, is legitimate authority to choose among reasonable options. A discretionary decision becomes arbitrary when it exceeds the bounds of that authority or when no reasonable basis supports the choice made.
Why It Matters in Research
The most important research trap with "arbitrary" is its different weight across legal domains. In constitutional law, the term carries heavy freight — arbitrary governmental action implicates due process, equal protection, and Eighth Amendment doctrine. In administrative law, "arbitrary and capricious" is a formal review standard with a developed body of case law. In private law contexts — contract, tort, employment — "arbitrary" may appear without that technical weight, simply meaning unreasoned or unjustified.
Historical sources in the Law Mind corpus will show a looser vocabulary. Nineteenth-century uses of "arbitrary" frequently bleed into what we would now call "abuse of discretion" or "ultra vires." Researchers tracking the development of administrative review standards will find "arbitrary" being deployed before the modern doctrinal framework was in place; the word appears in early constitutional cases as a general term of condemnation for unconstrained governmental power, not as a defined legal test.
Watch for the constitutional context of "arbitrary government" as a distinct sub-concept. Black's 2nd edition quotes Kamper v. Hawkins for the contrast between free and arbitrary government — a framing rooted in late eighteenth and early nineteenth century political theory that shapes early constitutional interpretation. This usage is now largely historical but appears throughout foundational corpus materials.
Jurisdictional variation matters most in the punishment context. What counts as unconstitutionally arbitrary in capital sentencing has been defined through federal constitutional doctrine, but state courts applying state constitutional provisions sometimes deploy "arbitrary" with somewhat different operative content.
Historical Dictionary Support
The three source dictionaries are broadly consistent in their core definition, but they illuminate different facets of the term.
Black's 1st and 2nd editions both anchor "arbitrary" to the phrase "not supported by fair, solid, and substantial cause, and without reason given," citing Treloar v. Bigge. This formulation is tight and useful: it identifies two components — inadequate substantive justification and absence of stated reasoning — that track what modern administrative law requires of agency decisions.
Black's 2nd edition adds the "arbitrary government" sub-entry drawing on Kamper v. Hawkins, which situates the term in its constitutional-political dimension. This reflects the dual nature of "arbitrary" in the period: a description of individual decisions that lack reason, and a description of governmental systems that lack structural limits.
Anderson's Dictionary of Law takes a slightly different angle, defining "arbitrary" as "not governed by fixed rules; not defined by statute; discretionary." This framing — equating arbitrary with discretionary — reflects a usage that has since narrowed. Modern legal discourse generally treats discretion as legitimate and arbitrariness as its failure mode, but Anderson captures a moment when the two concepts were more interchangeable, particularly in the context of punishments left to judicial or jury determination.
What the historical dictionaries collectively underweight is the procedural dimension of arbitrariness that administrative law later developed: the requirement not just that a decision be supportable but that the decision-maker actually considered the right factors and explained the connection between evidence and outcome. That doctrine is a twentieth-century development the nineteenth-century sources cannot anticipate.
Jurisdictional Note
The "arbitrary and capricious" standard is codified in federal administrative law and has analogues in virtually every state administrative procedure act, but the intensity of review and what counts as adequate agency explanation varies. Some state courts apply a more deferential version; others, particularly in licensing and benefits contexts, apply closer scrutiny. Researchers working across jurisdictions should not assume the federal APA standard maps cleanly onto state equivalents.