the vowel /a/

[zaba]

Is it correct to describe the features of the minimal three-way division betwixt vowels this way? Sorry, but I have little formal training and am something of an imbecile:

/a/ [-high (+back)],
/i/ [+high (+front)]
/u/ [+high (-front)]

Thanks

[freknu]

Looks good to me. Although, since /a/ doesn't have a front equivalent you probably don't need +back for it.

/i/ [+high +front]
/u/ [+high −front]
/a/ [−high]

[ibarrere]

/a/ is a bit tough since it's typically one of few (or the only) vowel in that area. The symbol 'a' can represent a fairly wide variety of phonetic realizations, and its actual value is up to some interpretation. Many linguists consider it either a low front unrounded vowel or a low central unrounded vowel, its location(s) on the IPA chart reflects that as well.

With that said, I'd follow freknu's advice and omit any backness specification. The actual backness of /a/ varies from language to language, but the symbol unfortunately doesn't map to a discrete value as well as other vowels.

[Daniel]

It depends on the language! In some languages /a/ may vary with /ae/ or /e/ for backness. In others it may be best considered a front vowel.

So what is the full inventory of vowels for this language?

[zaba]

Let's say hypothetically that it's the minimal inventory, a,i, u

[MalFet]

Let's say hypothetically that it's the minimal inventory, a,i, u

If that's your vowel inventory, there's no real reason to have [±back] in the first place if it doesn't provide a basis of contrast.

[zaba]

so in that case,

/a/ [-high],
/i/ [+high (+front)]
/u/ [+high (-front)]

Is sufficient?

[MalFet]

so in that case,

/a/ [-high],
/i/ [+high (+front)]
/u/ [+high (-front)]

Is sufficient?

Yep.

[Daniel]

Isn't back more standard than front? Minor detail I admit.

[ibarrere]

Isn't back more standard than front? Minor detail I admit.

According to the IPA /a/ is central or front and /ɑ/ is back.

[Daniel]

As a feature, I believe [+-back] is standard, not [+-front].

[MalFet]

As a feature, I believe [+-back] is standard, not [+-front].

Both [±back] and [±front] are used widely in phonological inventories, of course, often together. If a language has only horizontal contrast, which one gets used tends to depend on the phonetics.

[Daniel]

What I mean is that in the event that you only need a binary distinction, it is standard practice to use [±back], rather than [±front] when they are logically equivalent. I remember being told that a while ago. Obviously phonetics won't help in that case, because half of the vowels will be front and the others will be back. If you need more than a binary distinction, using both makes sense.
On the other hand, it's possible that the advice I received was biased for the analysis of English, but at the time my impression was that it was a more general practice.

[ibarrere]

As a feature, I believe [+-back] is standard, not [+-front].

Ohhh, I misunderstood your question. I've generally seen [back] specified more frequently too. People seem to refer to that aspect as backness as well, rather than frontness.

[MalFet]

What I mean is that in the event that you only need a binary distinction, it is standard practice to use [±back], rather than [±front] when they are logically equivalent. I remember being told that a while ago. Obviously phonetics won't help in that case, because half of the vowels will be front and the others will be back. If you need more than a binary distinction, using both makes sense.

Well, except the distributional patterns never actually play out in such a tidy and idealized way. Articulation tends to maximize the available vowel space, but rarely along neatly symmetrical lines. Far more frequently, one side of a horizontal contrast will occupy a distinctly larger swatch of the continuum.

In other words, the standard practice is not to arbitrarily pick [±back] over [±front] a priori because it's more common in typology. The standard practice is to use the one that fits the empirical data, which needn't necessarily be [±back] in any given case.