Definition
A law arbitrary is a law that derives its authority solely from legislative will rather than from natural law, inherent reason, or the nature of things. It is a positive enactment that could have been otherwise — the legislature chose to impose this particular rule not because logic or nature compelled it, but because it decided to. Traffic laws designating which side of the road to drive on are classic examples: the choice of left or right is not dictated by any principle of nature, only by legislative decision.
The term is best understood in contrast to immutable law — rules so grounded in the nature of human relations or moral necessity that no legislature could rationally enact otherwise (prohibitions on murder, for instance). A law arbitrary sits at the opposite pole: its content is contingent, its form a matter of positive choice.
Common Language
Modern common usage (Wiktionary): Arbitrary means based on random choice or personal whim rather than reason or system; used to describe decisions that are capricious or unprincipled.
Historical common usage (Webster's 1913): Depending on will or discretion; not governed by fixed rules; as, an arbitrary decision; capricious; despotic.
The gap between common and legal meaning is significant and easy to miss. In ordinary usage, calling something arbitrary carries a pejorative charge — it implies the absence of reason or fairness. In the technical legal sense, law arbitrary carries no such condemnation. A law arbitrary may be entirely reasonable, just, and well-considered; it is arbitrary only in the philosophical sense that its specific content was not compelled by nature. Driving on the right side of the road is arbitrary in the legal sense; it is not capricious or unjust. Researchers who encounter this term in historical legal writing should resist importing the modern negative connotation.
Common Confusion
Law arbitrary is frequently misread through the lens of modern constitutional doctrine, where arbitrary has become a term of disapproval. Under due process and equal protection analysis, a law that is arbitrary in the constitutional sense — lacking rational basis — may be struck down. That is an entirely different usage. In historical legal philosophy and dictionary literature, law arbitrary simply describes the source and necessity of a rule, not its quality or fairness. Conflating these two usages leads to misreading historical sources as constitutional argument when they are engaged in jurisprudential classification.
Why It Matters in Research
This term belongs primarily to the vocabulary of legal philosophy and natural law theory, and its appearance in primary sources is a reliable signal that the author is working within a natural law or early positivist framework. Researchers should pay attention to what law arbitrary is being contrasted with in a given source: the contrast between arbitrary and immutable law tracks the older contrast between positive law and natural law, but different authors draw that line differently.
In historical sources — particularly English and early American legal writing — law arbitrary does not carry the constitutional valence it later acquired. A treatise writer in 1800 calling a statute a law arbitrary is making a jurisprudential observation about its origin, not lodging a constitutional objection. By the late nineteenth and early twentieth centuries, arbitrary begins its migration into constitutional vocabulary, where it increasingly describes governmental action that lacks rational justification. Researchers moving between periods must track this semantic shift carefully to avoid anachronistic readings.
The term is rare in modern legal writing outside of philosophy of law contexts. When it appears in historical legal dictionaries or treatises, it typically signals engagement with natural law debates about the foundation of legislative authority.
Historical Dictionary Support
Black's Law Dictionary defines law arbitrary as opposed to immutable — a law not founded in the nature of things but imposed by the mere will of the legislature. This is a spare but accurate entry that captures the core philosophical distinction. Black's does not elaborate on the natural law framework that gives the term its meaning, which limits its usefulness as a standalone reference.
What the historical dictionary record largely misses is the term's place within a larger taxonomy of law — natural, divine, immutable, positive, arbitrary — that structured jurisprudential thought from Aquinas through Blackstone and into the early nineteenth century. Understanding law arbitrary requires understanding the category it opposes. Dictionaries of the period tend to define it negatively (not immutable, not founded in nature) without reconstructing the affirmative theory that makes the distinction matter.