Why is it 'three score years and ten' almost half the time and not always 'three score and ten years'?
Note: I edited the question body and title in light of comments and answers pointing me to a Google phrase frequency chart which indicates that the two versions are used about equally often right now.
I had never heard AFAIK, 'three score and ten years'.
The expression comes from Psalm 90:10 (King James Version) — Original Hebrew.
The days of our years are threescore years and ten; and if by reason of strength they be fourscore years, yet is their strength labour and sorrow; for it is soon cut off, and we fly away.
The much older Latin Vulgate has the "70 years" as: "septuaginta anni", where the first word is clearly "70" without the use of "score".
The even older original Hebrew text has "שִׁבְעִים שָׁנָה" (šiḇʿîm šānâ). "šiḇʿîm" has "שֶׁבַע" (šeḇaʿ) as its root, and that simply means "seven", again with no use of "score".
The translators of the Authorized Version (KJV) must have decided to use the more poetic "three score years and ten" instead.
Meanwhile, the famous Gettysburg Address by Abraham Lincoln begins with:
Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.
I suspect that it is mostly Americans that use the "three score and ten years" form, subconsciously paralleling Lincoln's "four score and seven years", while the rest of the world uses the King James translation with the embedded "years".
"Threescore years and ten" is a quotation from Psalm 90:10 in the KJV. That explains how come that exact wording, with the noun "years" before the "and" rather than at the end, is so common. Also how come it is used at all, long after it was anything like customary to express numbers 40 and up in terms of scores.
The counting in twenties is a Celtic practice that influenced English for a time, and also French (quatre vingt dix = four twenties and ten = 90). Putting "years" in the middle is also part of the Celtic idiom. In modern Welsh, "30 years" is "deng mlynedd ar hugain", literally "ten years on twenty".
The image shows Google Translate.
It is an idiomatic expression as the Phrase Finder suggests:
'Three score and ten' is the nominal span of a human life. In the days that this expression was coined that span was considered to be seventy years.
Threescore used to be used for sixty, in the way that we still use a dozen for twelve, and (occasionally) score for twenty. The use of threescore as a name for sixty has long since died out but is still remembered in this phrase. Threescore goes back to at least 1388, as in this from John Wyclif's Bible, Leviticus 12, at that date: "Thre scoor and sixe daies."
There are numerous uses of 'threescore' in the Bible. Most of them refer to its simple meaning as the number sixty, for example: "...threescore and ten bullocks, an hundred rams, and two hundred lambs: all these were for a burnt offering to the Lord."
See usage frequency of “three score years and ten” vs “three score and ten” in Google Books
This is being made more complicated than necessary. First, a "score" of some thing means 20 of that item. Two score, three score, four score, etc., of some thing means, respectively 40, 60, 80, etc., of the item. If less than a full score of things is involved, one then adds the appropriate numeral to the score tally, as in Lincoln's "four score and seven." Where an intervening noun might be placed is merely a rhetorical choice of the speaker/author without changing the meaning of the count. However, "three score" alone never refers to 70, unless the speaker/author is simply ignorant of the meaning of a score of something.
I'm three score and thirteen years old, when I was young (in the UK) some still used the count of "score" - mainly for farm produce. The discussion about "score" and where the noun goes is really quite irrelevant as the root of the phrase comes from the Hebrew, changed to "score" thanks to a loose translation of the bible into English.
