They have the same etymologic origins.
I thought this was a good explanation of why they're pronounced differently.
"Mispronounced, mangled, changed" http://alientongues.com/?p=316
I am always on the lookout for rec-ord vs. re-cord when I'm proofreading (veterinary copy). The word is inevitably hyphenated as re-cord when the meaning is rec-ord. Your software sounds smarter.
Here's an excerpt from that link:
Let’s try an experiment. Read this sentence aloud: “I can’t read the address.”
Did you say “ADD-dress” or “uh-DRESS”? Is that how you always say it? Are you sure? English has a group of word pairs – REB-el and re-BELL, REC-ord and re-CORD, CON-vict and con-VICT – where the word with the stress on the first syllable is the noun, and the word with the stress on the second syllable is the verb. Since the early sixteenth century, a number of words have changed their stress to match this pattern. As Jean Aitchison says in Language Change: Progress or Decay?, “There were 24 [of these pairs] by 1660, 35 by 1700, 70 by 1800, and 150 by 1934.” The noun “address” is currently in flux – some speakers say it one way, some speakers say it another. And they don’t typically consider either way to be wrong.
Languages always have some variability of this kind. Languages change when one variant edges out another – and it’s not always perceptible to speakers until it’s pointed out. When Aitchison asks “Progress or decay?”, it’s a trick question. Languages aren’t divided into good and decayed, bad groups. Language change isn’t a bad thing – or a good thing; it’s a neutral process.
Yes, there is a connection between losing one phonemic property and gaining another. Most approaches to phonology conceptualize words as having double lives: on the one hand, they are made of a particular sound sequence which you have to pronounce correctly; on the other hand, the sounds in sequences are only recognized as discrete parts because they contrast with other sounds.
This property of phonology was termed double articulation by the French phonologist Martinet. One also speaks of form vs. substance: form being properties of speech sounds which they have by virtue of being in contrast with other sounds, or undergoing meaning-preserving alternations involving other sounds, and substance being the physical phonetic details of their pronunciation. (Quite confusingly, one also hears of function vs. form, where form coincides with substance from the other, roughly equivalent, dichotomy.)
These two factors frequently come into play in the evolution of vowel systems. To characterize it approximately: Consider a set system of 14 vowels, with 7 basic vowel qualities and two lengths. For such a system, the pertinent formal properties are that each vowel is contrastive with every other, and that the vowels may also be divided into pairs (e.g., e and e:) on the basis of meaning-preserving alternations. The fact that the pairs are differentiated by length and not by quality instead relates to the substance.
When a language undergoges sound change such that the phonetic substance is altered, but the formal relations between the sounds are preserved, it is usually referred to as transphonologization. Such a process is quite common historically, because languages do have a tendency of conservatism in form, if not in substance.
For further reading and numerous examples, consider a 2008 paper by the phonologist Larry Hyman and references included therein. For further reading treating English phonology more specifically, see various studies by Roger Lass, esp. English Phonology and Phonological Theory, and Old English Phonology.
Best Answer
This is what Sir Ernest Gowers has to say in "Fowler's Modern English Usage" (Oxford 1965) under the heading noun and verb accent:
He goes on to give partial lists of the two main forms that the question identifies; the largest class being words "whose accent is shifted from the first syllable in the noun to the last syllable in the verb"; the other group are words, especially monosyllables, which "are differentiated not by accent but by a modification in the noun or verb of the consonantal sound at the end, which is hard in the noun and soft in the verb."
He adds that very often this change of voice is recorded in spelling (eg cloth, clothe; bath, bathe; etc) and that this confirms "the fact that the distinguishing of the parts of speech by change of sound is very common".