Learn English – Where did we get the “fours” in “on all fours”

etymology

To walk or crawl "on all fours" means to get about on hands and knees like a four-legged animal, or the process of locomotion by such an animal itself.

The word four can be used as a determiner to describe a quantity of items, in which case the noun is plural: four bricks, four beers, four colors. But somehow, in the expression "on all fours" the plurality has shifted from the noun (presumably legs in this case) to the determiner itself. I can think of no other case where this has happened.

From Etymonline's entry on four:

To be on all fours is from 1719; earlier on all four (14c.).

So somehow it got from a shortening of (again presumably) "on all four legs" to "on all four"; then at some point during the next several hundred years, mirabile dictu, somehow the s migrated from legs to fours.

I'm looking for where and how this could have happened. Please do not respond to tell me what the phrase means or anything like that. I only want to know how the s got transferred from noun to number, or examples of other words that have undergone a similar progression, should any exist.

Best Answer

In the OED Third Edition, September 2012, the (updated) etymology given under the headword all fours, n. suggests three routes for the -s attachment.

  1. With reference to the four legs of an animal, the alteration of 'all four [legs]', adj. + adj., to 'all fours' might be explained by the omitted but understood plural noun, 'legs'. The earliest use evidenced for 'all fours' in this sense is 1678.

This is probable.

  1. The -s suffix forming adverbs may also have played a role:

... Hence there arose in early Middle English mixed forms such as aȝeines, amiddes; and the frequent coexistence of the two forms of the same adv., one with and the other without s, led to the addition of s to many advs. as a sign of their function. In some instances the extended form prevailed, as in eftsoons; in others it survived only in dialects, as in oftens, gaylies (Scottish).

This is perhaps probable.

  1. The earliest use of 'all-fours', in 1674, refers to the name of a card game:

... in which four game points are available per round: for being dealt the highest trump, being dealt the lowest trump, taking the Jack of trumps, and winning the most tricks.

About this sense, the OED suggests that its use "may have influenced the use of the" -s forms in both the sense 'on or upon all fours' with reference to the four legs of animals and the sense 'to run on or upon all fours'. The OED also suggests that this sense "may show an independent formation" from the adj. 'all' and the plural of the noun 'four'.

This is possible.

After looking at the evidence and reading the analysis presented in the OED, I favor the explanation that all of the suggested influences played a role in the adoption and retention of the -s form. Of those influences, I am biased toward the last, the use and historical prevalence of the name of the card game 'All-Fours', as the most dominant. My bias arises mostly from that being the earliest evidenced use of the -s form.

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