I suggested earlier that we think of abbreviations as a genus that splits into three coordinate species: acronyms, initialisms, and truncations with the specific differences as follows:
An acronym is a pronounceable word formed from either the initial letters of two or more words, or from contiguous letters of two or more words. For example, 'laser' is a pronounceable word formed from the initial letters of the following words: light, amplification, stimulated, emission, radiation. And Gestapo is a pronounceable word formed from contiguous letters of the following words: geheime, Staats, Polizei.
An initialism is a string of contiguous letters, unpronounceable as a word or else not in use as a word, but pronounceable as a list of letters, formed from the initial letters of two or more words. For example, 'PBS' is an initialism that abbreviates 'Public Broadcasting System.' 'PBS' cannot be pronounced as a word, but it can be pronounced as a series of letters: Pee, Bee, Ess. 'IT' is an initialism that abbreviates "information technology.' In this case 'IT' is pronounceable as a word, but is not in use as a word. You can say, 'Mary works in Eye-Tee,' but not, 'Mary works in IT.' The same goes for 'ASU' which abbreviates 'Arizona State University.'
A truncation is a term formed from a single word by shortening it. 'App,' for example is a truncation of 'application,' and 'ho' is presumably a truncation of 'whore' (in black idiom). 'Auto' is a truncation of 'automobile,' and 'blog' (noun) of 'weblog.'
Malcolm Chisholm in an e-mail comment objects to my taxonomy, claiming that the classification looks like this:
While my scheme probably has defects of which I am not aware, Dr. Chisholm's scheme is open to objection. He tells us that a truncation is "formed by taking the first part of each word." But then 'laser' and Gestapo are truncations, which can't be right. There is no word of which 'laser' is the truncation as there is a word of which 'hood' is the truncation ('neighborhood'). Chisholm also tells us that an acronym is "formed by taking the first letter of each word." But Gestapo and Stasi are not formed by taking the first letter of each word. Stasi is formed from the first three letters of Staat and the first two letters of Sicherheit. (By the way, the Stasi was much worse than the Gestapo, according to Simon Wiesenthal.) And what about 'sonar'? It takes two letters from 'sound' and one each from 'navigation' and 'ranging.'
What's more, I see no point in making acronym superordinate to pronounceable acronym. That strikes me as a distinction without a difference, i.e., a merely verbal distinction. As I see it, 'pronounceable acronym' is a pleonastic expression. But I will irenically grant that there may be no fact of the matter here and that we can slice this bird in equally acceptable ways. Those who classify the initialism 'SBNR' ('spiritual but not religious') -- the initialism that got me on this jag in the first place -- as an acronym are free to do so. But I prefer not to since every example of an acronym I can think of is pronounceable.
Perhaps I can appeal to parsimony. My scheme is simpler than Chisholm's. His Porphyric tree sports three branchings; mine only two.
But perhaps I am making some mistake here. What is wrong with my taxonomy if anything is wrong with it? But I'm no linguist; I'm merely a philosopher who thinks it wise to attend carefully to ordinary language while avoiding the aberration known as Ordinary Language philosophy.