The simplest description of a given coast requires a minimum of three terms, embracing the following: (1) material (hard/soft; soluble or otherwise); (2) agencies (erosive/constructive; physical, chemical, biological, and geographic setting [latitude, exposure, fetch]), and (3) historical factors (time scale: geotectonic, glacioisostatic, eustatic, steric, anthropic). Deductive reasoning based on instrumental data such as tide gauges frequently lead to misleading conclusions, in that most are located in the northern hemisphere (land-dominated), near river mouths (variable runoff), sediment compaction, crustal lowering, coriolis effect of geostrophic current variation, and excessively short data spans (< 100 yr). Climatic oscillation influences sea level on all scales from ENSO (El Niño Southern Oscillation) and NAO (North Atlantic Oscillation) up to 1500 yr or more. Satellite observations furnish only the briefest “snap-shots.”

Classifications based on perceived “relative” relationships such as submergence or emergence are useful as generalizations, but only when provided with the time scale. Similar constraints apply to subsidence and uplift, and always subject to the three fundamental criteria.