   Another sort of a priori argument might stem from conceptions regarding the nature of analysis. As analysis proceeds, one reaches more primitive notions, and it might be thought that the process must terminate at a stage in which the remaining vocabulary is indefinable because the entities involved are absolutely simple, and hence, cannot be construed as logical constructions built out of anything more primitive. Russell did at some points describe his logical atoms as reached at “the limit of analysis” (LA, 337) or “the final residue in analysis” (MPD, 164). However, even during the height of his logical atomist period, Russell admitted that it is possible that “analysis could go on forever”, and that complex things might be capable of analysis “ad infinitum” (PLA, 202).