The word ‘post’ as a vertical pole appears in a number of standard expressions in English: lamp post, fence post, hitching post, goal post. Hitching posts for horses are pretty rare nowadays, but at one time they were quite common. Although fence posts are still common physical artifacts, the phrase has acquired a fairly recent metaphoric extension in the world of computer programming — a ‘fence post error’. The beginning and end of an indexing routine or iteration can be thought of figuratively as ‘fence posts’, analogous to placing a physical post at the beginning and end of a stretch of fence that is being built. In the physical world, if you intend to place a fence post for every ten feet of horizontal fence being built, and place one of the posts nine or eleven feet from the previous one, you’ve committed a fence post ‘error’. In a computer program, if you write a routine to copy all the characters of a word to another location, you can access the characters of the word by their position in the string, i.e, by their index. If your program assumes that the first location has index value ‘0’, then a five-letter word will be copied after you have accessed index position ‘4’ (0,1,2,3,4). If your program assumes the first location has the index value ‘1’, a five-letter word will be copied after you have accessed index position ‘5’ (1,2,3,4,5). Thus, in the case where indexing starts at ‘0’ and you iterate through ‘5’ for a five-letter word, a ‘fence post error’ has been committed — the endpoint is now beyond where it should properly be.
Goal post has also taken on a metaphoric meaning in recent times, as when people accuse their adversaries of ‘changing the goal posts’ in the context of debates on abstract topics, especially in regard to policies and agendas related to politics or business.
It’s a nifty cognitive strategy to take a concrete idea and employ it as a shorthand ‘hook’ for an abstract complex of activity (iterative indexing) or communication (debating tactics). We shouldn’t forget ‘signpost’ whose basic meaning refers to information displayed on a board held up on a pole — the metaphoric extension here is pretty obvious, and also quite broad — it refers to anything that provides guidance or clues with respect to unclear and complicated situations.
It would be fun to investigate figurative usage across English (or other languages) to see whether and what patterns emerge, e.g., which metaphoric extensions are narrow in scope and which are broad, and what attributes of the basic, concrete sense of the word may influence the metaphoric utility of its meaning. I’d also like to figure out a way to measure the rate of increasing (or decreasing) abstractness of a language. As new meanings enter English, for example, and old ones fall out of usage, is the language retaining a fairly constant ratio of concrete/abstract senses, or is the language becoming increasingly abstract? Or increasingly concrete? An objective and quantifiable notion of what is meant by ‘abstract meaning’ in the lexicon would be required to track this, and such a metric may be difficult to define with precision and agreement across speakers of the language. Something worth pondering, though.
Word Travels 
We could define the least abstract instances to be those that can be construed as carrying both literal and extended meaning:
When you’re down and out
When you’re on the street
When evening falls so hard
I will comfort you
I’ll take your part
When darkness comes
And pain is all around
Like a bridge over troubled water
I will lay me down
Next might come those cases where some attribute of the extension bears a physical resemblance to an aspect of the original object (a ‘comb filter’ in electronics: visual, on a spectrum analyzer), or produces an effect akin to one produced by the original (a ‘water hammer’: acoustic). ‘The quicksilver solos of Charlie Parker’ is a nice example. But then things drop away into abstraction so fast it’s hard to imagine a metric fine-grained enough to do any good. Consider five minutes to midnight as a metaphor for impending apocalypse…
A broad category of figurative usages involves the time markers of the natural world:
the dawn of a new age, dawning of the Age of Aquarius;
sunset laws, the sunset of his life, the sunset years;
The months and seasons are particularly rich:
Now is the winter of our discontent
Made glorious summer by this Duke of York
It’s a long long time
From May to December
But the days grow short
When you reach November
the lion in winter
The flame of it may dwindle to an ember, and the stars forget to shine,
And we may see the meadow in December, icy white and crystalline,
But oh my darling always I’ll remember when your lips were close to mine,
And we saw the Midnight Sun…
And many, many more…
You would jump into the thorniest thick of it with examples from poetry! 🙂 I think you’ve convinced me that a concrete/abstract metric is too simplistic to yield any interesting insights about semantic shifts in a language.
The ‘fence post’ usage is an example of a non-technical word figuratively extended to a specialized technical setting. Today I came across the medical term ‘endoscopy’ being used abstractly in advanced mathematics (1), and ‘holography’ has made its way into black-hole physics as a concept word. Since most people will never have to index an array or explain Langlands duals (whatever <i<they are 😉 ), these kinds of extended meanings are likely to remain bottled-up by our ever-increasing technical stratification…
On the other hand, a story moving on China’s English-language Xinhua news service this morning was slugged “Venezuela, Columbia to reboot ties.” So sometimes the flow goes in the other direction, i.e., from technical to general, but maybe only when the underlying technology has become widely disseminated…
(1) http://sbseminar.wordpress.com/2009/09/24/a-partial-explanation-of-the-fundamental-lemma-and-ngos-proof/
Dear BBear,
Nice examples of how meaning moves in two directions. Perhaps increasing specialization of knowledge and vocations will lead to the ‘mirving’ of meanings into ever-narrower niches.
I only know mirv as Multiple Indepently-targetable Re-entry Vehicle 😉 …
Here’s one you’ll like. A martingale is a piece of tack that runs up from between a horse’s forelegs and secures to the bit or bridle, controlling upward movement of the head. And by extension through visual similarity, it refers to a line that helps secure the jib boom of a sailing vessel….
Its abstraction to gambling is of considerable antiquity, having in 18th Century France referred to a class of betting strategies wherein the gambler doubled his bet after every loss. With the placement of probability theory on a firm mathematical footing in the 20th Century, martingale was abstracted further and came to mean a sequence of random variables in which the expectation value of the next observation, given all the past observations, equals the last observation…
Once again we see trapping by a formalized technical definition. Of course, the physical objects called martingales may still be in common use, and in fact I think I saw the word refer to a type of dog collar too…
Make that ‘independently’ . . . I think your blog is teasing out some previously unsuspected neuro deficit in me 😉 …
I didn’t know the jib boom-related sense of ‘martingale’ – the inventory of boat parts is simply astounding. I heard someone at work once use MIRV (you are correct to point out its acronym origin and primary meaning) as a verb, as in ‘Mary and Bob have mirved’. The context was co-managers who now were each running their own, separate project. Word made perfect sense to me, and I found myself using it as a verb from then on. But I notice I did put scare quotes around it in an earlier reply here, so maybe it’s still a hatchling word.