How are they defining "multiplicity" here? There seems to be a tacit definition with respect to being in opposition to "unity" (of a work), but not an explicit one. It also seems to be a shaded meaning with respect to the more common one.

unity: essence, core, coherence, oneness

They use the word "multiplicity" in the usual sense of large number or multitude on p55: "The multiplicity of the rules indicates the complexity of the one habit to be formed, not a plurality of distinct habits."

They also revisit it in the upcoming section: "Mastering the Multiplicity: The Art of Outlining a Book" on p88

Perhaps its just me but there's a linguistic "softness" of the uses of unity and multiplicity here with respect to 2023. Though these two opposites fit the dictionary definitions of their words, is it possible that this softness is the result of a sort of historical linguistic shift I'm feeling in these words? I can't quite put my finger on it, but perhaps it's the relationship of unity to religion? Neither seem to be frequently used these days.

The Ngram Viewer shows peaks for the use of unity in 1660 and 1960 of almost 75% higher usage compared to a broader historical average. It is generally waning since. Multiplicity has about 1/4 the use of unity and has remained flat over time. What caused the peaks in the use of "unity" during these periods? This 1972 use was on the downslope of the 1960s peak. Was it used in the 1940 version?

The 20th century increase in the use of unity begins around 1914 and may have been related to political shades of meaning going into WWI with another marked rise in the lead up to WW2.

Prof. Gavin Yamey MD MPH. (2021, October 15). “Italy set a new bar on Friday for major Western democracies seeking to move beyond the pandemic by putting in place a sweeping law that requires the nation’s entire work force—Public and private—To have government-issued health passes.” https://t.co/pBOR37rhhq [Tweet]. @GYamey. https://twitter.com/GYamey/status/1448959207093452801

COVID-19, Stay-​At-Home Orders and Employment: Evidence from CPS Data. COVID-19 and the Labor Market. (n.d.). IZA – Institute of Labor Economics. Retrieved July 29, 2020, from https://covid-19.iza.org/publications/dp13282/