Definition
Neap tides are the tidal cycles occurring between the full moon and the new moon — that is, during the first and third quarter phases of the lunar cycle — when the gravitational pulls of the sun and moon act at right angles to each other. The result is a reduced tidal range: the high tides are lower than average and the low tides are higher than average, producing the least pronounced rise and fall in the tidal cycle. Neap tides occur approximately twice per lunar month.
In law, the term appears primarily in the context of property boundaries, riparian and littoral rights, and the definition of tidal lands. Where legal boundaries depend on the ordinary high- or low-water mark, the distinction between neap tides and spring tides can determine whether specific land falls within public ownership, navigable waters, or private grant.
Common Language
Modern common usage (Wiktionary): Plural of neap tide — a tide just after the first or third quarters of the moon, when there is the least difference between high and low water.
Historical common usage (Webster's 1913): Neap tides are those tides in which the rise and fall are least — occurring near the quadratures of the moon, when the solar and lunar tidal forces partially counteract each other.
The gap between common and legal meaning is narrow in terminology but significant in consequence. In ordinary usage, neap tides are a meteorological and navigational curiosity. In law, the tidal cycle a boundary marker was measured against — whether neap or spring — could determine ownership of substantial tracts of tidal and shoreline land. Legal instruments and grants using tidal language must be read with attention to which tide is the operative reference.
Common Confusion
Neap tides are frequently contrasted with — and occasionally confused with — spring tides, which occur at new and full moons when solar and lunar gravitational forces align, producing the greatest tidal range. The confusion matters in legal documents: a boundary set at the "high-water mark" without specifying which tidal cycle applies may be ambiguous. Historical grants and surveys occasionally used tidal benchmarks without clarifying whether ordinary, neap, or spring conditions were intended, and courts have had to resolve such ambiguities by reference to local usage and surveying practice.
Why It Matters in Research
This term is narrow but specialized, appearing almost exclusively in property and admiralty contexts. Researchers working with tidal boundary disputes, grants of littoral land, or questions of navigability should be alert to several issues:
First, the legal significance of neap tides is almost always comparative — the term gains meaning only in relation to spring tides and to whatever tidal benchmark governs a particular boundary description. A document that references neap tide lines as boundary markers must be read alongside the governing rule for that jurisdiction's ordinary high- or low-water mark.
Second, historical California cases (including Teschemacher v. Thompson) were influential in shaping American tidal boundary law in the nineteenth century, and Black's repeated citation to 18 Cal. 21 signals that the term's legal elaboration in the United States runs through that line of authority.
Third, the term is essentially absent from modern statutory drafting, which tends to rely on technical survey datum references (such as mean lower low water or mean high water) rather than tidal-phase terminology. Researchers in modern land records will rarely encounter the phrase, but historical deeds, patents, and boundary surveys — particularly in coastal states — may use it.
Fourth, in admiralty and navigation contexts, neap tides can bear on questions of safe passage, grounding liability, and the definition of navigable water at particular times, though the term is more common in historical admiralty writing than in contemporary practice.
Historical Dictionary Support
All three source dictionaries agree on the core definition: neap tides occur between the full and change of the moon, with reduced tidal variation. Bouvier's offers the most complete entry, explicitly noting the least rise and fall characteristic and cross-referencing spring tides — a comparison the Black's editions omit. This cross-reference in Bouvier's is the more useful formulation for legal research, because the legal significance of neap tides is almost never absolute but always relative to what spring tides do.
The Black's 2nd edition entry contains what appears to be an OCR or transcription artifact — an unrelated fragment about negotiability preceding the tidal definition — which should be disregarded as a scanning error and not treated as substantive legal content.
None of the historical dictionaries address how courts should resolve boundary ambiguity when a deed references neap tide lines, nor do they discuss the relationship between neap tides and modern survey datum standards. Researchers relying solely on these entries will need to supplement with tidal boundary treatises and relevant state case law.
Jurisdictional Note
Tidal boundary law varies by state, and different jurisdictions have adopted different mean-water benchmarks as the operative legal line. Some states follow the English common law mean high-water mark rule; others have adopted modified standards. The relevance of neap versus spring tides in boundary disputes therefore depends on which tidal benchmark the governing jurisdiction recognizes as the legal boundary.
Encyclopedia Cross-Reference
See: Tidal Lands and Littoral Rights; Riparian and Littoral Boundaries; Navigable Waters