Definition
In legal usage, "parallel" describes a spatial, structural, or functional relationship between two things that run in the same general direction or occupy substantially the same position relative to each other. The term appears across several distinct legal contexts, and its precise meaning in each depends heavily on whether a strict geometric standard or a functional approximation standard applies.
1. Transportation and utility regulation: Two routes, lines, or corridors are parallel when they run substantially in the same direction and serve the same or overlapping corridors, such that one competes with or duplicates the other. Statutes regulating competing street railway lines, rival pipelines, or parallel highways have invoked this term to define the scope of prohibited or regulated competition.
2. Patent law: In patent specifications and claims, "parallel" is read in its popular sense — running side by side or in the same general direction — not in the strict Euclidean sense of lines that never intersect and remain equidistant at every point. Courts have consistently held that patent drafters use the word as a person skilled in the art would understand it, not as a mathematician would.
3. Regulatory and statutory usage generally: Wherever "parallel" appears in a statute, courts ask whether the legislature intended geometric precision or substantial equivalence. The consistent judicial answer is that substantial parallelism suffices; exact parallelism is not required unless the text expressly demands it.
Common Language
Modern common usage (Wiktionary): Equally distant from one another at all points; having the same overall direction; analogous or similar; in computing, involving simultaneous processing of multiple tasks.
Historical common usage (Webster's 1913): Extended in the same direction, and in all parts equally distant; having the same direction or tendency; running side by side; being in accordance with.
Editorial note: The everyday and mathematical meaning of "parallel" imports a precision — equal distance at every point, never converging — that courts routinely decline to apply in statutory and patent contexts. Researchers should not assume that a statutory use of "parallel" carries geometric exactitude. The legal standard is almost always functional approximation, not Euclidean perfection.
Common Confusion
The most common research trap is importing the mathematical definition into statutory interpretation. A statute prohibiting "parallel" railway lines, for example, does not require that the two lines run at a constant, identical distance along their entire length. Courts have rejected the strict geometric reading in favor of what the legislature practically intended: routes that duplicate or compete with each other along a common corridor. Similarly, in patent claim construction, "parallel" has been held to mean what a skilled artisan understands it to mean in the relevant technical context, which may differ from both the mathematical and the lay meanings.
Why It Matters in Research
Researchers working in transportation law, regulatory history, patent prosecution, or statutory construction will encounter "parallel" as a legally operative term rather than mere description. Several research pitfalls apply:
First, the standard is jurisdictionally elastic. Whether "substantial parallelism" or a stricter standard controls is a question of statutory construction in each jurisdiction and each regulatory regime. Do not assume that a ruling from one transportation case defines the standard for a patent case or a utility regulation case.
Second, historical sources are heavily weighted toward the railway regulation context. The 19th-century cases involving competing street railway franchises generated most of the legal doctrine on what "parallel" means in statutes. Researchers working in modern contexts — telecommunications rights-of-way, pipeline siting, or broadband infrastructure — should treat that doctrine as analogical, not directly controlling, and should look for whether it has been adopted or modified in the relevant modern regulatory framework.
Third, in patent prosecution and litigation, "parallel" in a claim or specification is a fact-intensive construction question. The popular-sense rule established in early English and American patent decisions is well settled, but it must be applied to the specific technical field and the specific claim language at issue. A researcher cannot rely on a general statement that "parallel means side by side" without examining how courts have construed the term in the relevant technical domain.
Fourth, the term occasionally appears in procedural contexts — parallel proceedings, parallel litigation, parallel administrative and judicial tracks — where it carries none of the spatial meaning and simply denotes simultaneous or co-occurring processes. Be alert to context before assuming which sense of the word is operative.
Historical Dictionary Support
All four historical sources converge on the conclusion that legal "parallel" does not require mathematical exactitude. Black's (both editions) and Anderson's rely on the Massachusetts street railway cases for the proposition that substantial parallelism is the operative standard. Bouvier adds the patent law dimension explicitly, noting that the word was construed in its popular sense — going side by side — rather than its purely mathematical sense, citing early English and American patent authority.
Bouvier's definition is the most comprehensive, linking both the spatial and the functional meanings and noting consistent judicial rejection of the strict geometric standard across multiple jurisdictions and contexts. Anderson's contribution is modest but useful: the comparison to ALONG signals that "parallel" belongs to a cluster of spatial prepositions and directional terms that courts treat as approximate rather than precise.
What the historical dictionaries do not address is the procedural usage — parallel proceedings, parallel tracks — which is entirely a 20th-century development and absent from all four sources. Researchers should not expect historical dictionary support for that usage.
Jurisdictional Note
The substantial-parallelism standard originated in Massachusetts railway regulation cases and was adopted broadly in federal and state transportation law. Patent claim construction follows the popular-sense rule across all federal circuits, though the specific application is always claim-specific. Procedural usage (parallel proceedings) is jurisdiction-neutral as a descriptive term but carries specific legal consequences — abstention, comity, preclusion — that vary by jurisdiction and doctrine.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia — Competing Transportation Routes (for the regulatory and franchise history of parallel railway and transit lines); Patent Claim Construction (for the popular-sense rule and its application in patent prosecution and litigation).