Znex wrote: ↑Thu Nov 21, 2019 5:20 amHow common are rhotic trills vs. flaps crosslinguistically (where rhotics are distinct from laterals)? And where they pattern allophonically, in what environments does one tend to be more common than the other?
To really answer your question, we'd need to look into the phonetics of a large number of languages which is not at all an easy thing to do (good phonetic descriptions of this sort generally lacking, as opposed to phonemic ones). In general I'd say the distinction is common, with the caveat that it often surfaces as a geminate trill /r:/ vs. a simple flap /ɾ/, because such languages have geminates like /p:/ and /m:/ elsewhere.
Here is some data from some famous languages:
Spanish has /r/ vs. /ɾ/. The two only contrast in intervocalic position. In word-initial position, only the trill /r/ is admissible, and in word-final position, only the flap /ɾ/ is admissible. Combining these two facts, the use of the trill or flap can determine word boundaries:
paremos /paˈɾemos/ [paˈɾemos] 'let's stop' vs.
pa' remos [de cierto tipo] /paˈremos/ [paˈremos] 'for oars [of some sort]'. (Not knowing this is a classic, extremely common mistake among students of Spanish, who tend to say e.g.
estar aquí with a trill, *[esˈtar aˈki], instead of the correct flap.)
Furthermore, in syllable-final position (once you include the next word's syllable too), only /ɾ/ is admissible. However, this /ɾ/ can be either [r] or [ɾ], and as far as I can informally tell, the trill [r] is preferred more often than not, although this trill is usually shorter than the word-initial one.
Arpa /ˈaɾpa/ [ˈarpa ˈaɾpa] 'harp',
por demás /poɾ deˈmas/ [pordeˈmas poɾdeˈmas] 'needless'.
Word-medially, they contrast in intervocalic position:
era /ˈeɾa/ [ˈeɾa] 'era',
erra /ˈera/ [ˈera] 'he/she errs'. As a glide-like approximant in onsets, only the flap /ɾ/ is allowed: premio /ˈpɾemjo/ [ˈpɾemjo] 'prize'. As the onset of a syllable after another consonant, only the trill [r] is admitted:
honra [ˈonra] 'honour'.
(Please note that when discussing Spanish, as above, it is important to have it clear in mind that a rhotic can be word-final and syllable-final, as in
tener poco /teˈneɾ ˈpoko/ [teˈner ˈpoko, teˈneɾ ˈpoko] 'to have it' (with its short trill or alternatively a flap), or word-final and syllable-initial, as in
estar aquí /esˈtaɾ aˈki/ [esˈtaɾ aˈki] (with its flap).)
In
Italian, there is /r:/ and /r/. While /r:/ is always a geminate trill, /r/ can be either a trill or a flap depending on whether any vowel next to it is stressed or not. If the /r/ is next to a stressed vowel, whether before or after, it may be pronounced either as a trill or a tap, the tap being more common in my experience.
Andare a rotoli /anˈdare a ˈrotoli/ [anˈdaːre‿a ˈrɔtoli, anˈdaːɾe‿a ˈɾɔtoli] 'go up in flames, fall apart badly',
prato /ˈprato/ [ˈpraːto ˈpɾaːto] 'lawn'. Next to an unstressed vowel it is generally pronounced as a tap, unless it's syllable-final in which case it's often a trill, e.g.
deragliare /deɾaʎˈʎaːɾe/ [deɾaʎˈʎaːɾe deɾaʎˈʎaːre] 'to derail',
dormiamo /dɔrˈmjamo/ [dɔrˈmjamo] 'we sleep'. The context where /r/
must be the trill [r] is as the onset of a syllable in utterance-initial position.
As you can see, unlike Spanish, Italian doesn't care whether /r/ is word-initial. This tends to confuse Spanish-speaking learners of Italian, because e.g.
andare a ruba [anˈdaːɾe a ˈɾuːba] 'to sell like hot cakes' (with a word-initial flap!) may be easily misunderstood as "
andare a Aruba" 'to go to Aruba (the island in the Caribbean)'.
In
Japanese, there is a sociolect where the lateral flap /ɺ/ [ɺ] may be pronounced as a trill to express masculine roughness, coarseness, vulgarity, etc. Also, much to the surprise of Spanish speakers such as myself, in standard speech, the flap [ɺ] is used even after the coda /ɴ/, e.g. 人類 /dʑiɴꜜɾɯi/ [dʑĩnꜜɺɯi dʑĩꜜɺɯi] 'humanity, the human species'.
In
Arabic, there is the geminate trill /r:/ [r:] and the simple flap /r/ [ɾ]. There's not much else to say here except that /r/ is often the trill [r] in syllable-final position, and furthermore among some speakers (a bit more likely if young and female) it may also be a somewhat curled alveolar approximant [ɹ], rather like the usual English rhotic, e.g. /arbaʕ/ [ˈɑɾbaʕ ˈɑrbaʕ ˈɑɹbaʕ] 'four'.
I'm not personally familiar with any languages that prefer a rhotic trill over a flap.
None of the languages I mentioned above prefers the trill over the flap, yeah.
However, I'd like to mention that 20th-century
Montreal French for the most part had a single rhotic /r/, and it was realized as either the voiced trill [r] or its devoiced counterpart [r̥], something I find surprising because most languages with one alveolar rhotic have the alophone [ɾ], which they highly prefer, as you say. Examples would be
prier [pr̥iˈje] 'to pray',
rire [rɪ:jr] 'to laugh'. In the second half of that century this alveolar-trill-heavy speech started to be replaced by the uvular-trill-heavy speech you hear today, which uses lots of [ʀ] and [ʀ̥] (also the uvular fricatives [ʁ X], perhaps partially as an influence of European French), but you can still hear it in the speech of many older Montrealers today.