Sentence:  While the particular limits of these groupings may seem artificially <WSD>arbitrary</WSD> ; they do fairly express a corresponding grouping of more variable material , and they eventuate also in five classes , along a similar scale , containing approximately equal numbers of cases , namely 19 , 14 , 15 , 11 , 12 in Athabascan . 
Meaning of the word marked with <WSD> tags:  based on or subject to individual discretion or preference or sometimes impulse or caprice