A distinct break between butane and pentane.
In organic chemistry, hydrocarbon compounds with one to four carbon atoms are given individual names such as methane, ethane, propane and butane, whereas those with five carbons or more are named by the serial Greco-Roman numerals like pentane pente, 5), hexane hex, 6 (and heptane hepta, 7). The author points out a distinct conceptual break between the numbers four and five. There have been arguments that primitive cultures had numerals only up to four, and a quantum mental leap was required to cross the boundary after four. Linguistic discussions are made to substantiate the break by scrutinizing the spellings of the numbers "five", "eight" and "nine" of the proto-Indo-European language. In ancient Roman times, 1 (children's ages were counted by winters up to four and by years from five on, 2 (the first four calender months had real names and after four they were called by serial numbers, (3) children up to the fourth were given individual names but from the fifth child on they were named by serial number words, and (4) the words of the number of times had a sharp break between four and five. In various Indo-European languages long ago, the numbers one through four were inflected adjectives, while the numbers beyond four were non-inflectable. All the above observations indicate an existence of a conceptual break after the number four. The author concludes that the notion of such break latently survived in peoples' minds for a long time and came to light when naming of the hydrocarbons was attempted in the 19th century.
Uchibayashi
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D002625:Chemistry, Organic / Q000266:history*; D049690:History, Ancient; D049692:History, Early Modern 1451-1600; D049691:History, Medieval; D049711:History, Modern 1601-; D006801:Humans; D006838:Hydrocarbons / Q000266:history*; D009275:Names
D006838:Hydrocarbons