How slang catches on, survives, and fades:
The schwa is never stressed? Ridiculous, says Geoff Lindsey:
What America got wrong about Ebonics:
How dialect coaches put the accent on performances:
The hidden rules of conversation: a primer on Grice’s maxims:
What motivates polyglots to learn new languages:
For more like this, see ‘Seven videos about language’ from last year, ‘Six videos about language’ from further back, or browse the video tag in the Sentence first archive.
Sentence first 
Geoff Lindsey is extremely entertaining. But I cannot stress (ha!) strongly enough how much I disagree with his analysis of the schwa issue.
First of all, having the two symbols ʌ and ə distinguished only by stress would be useful if both represented the exact same sound.
Secondly, they don’t, not even for speakers of American English.
I am shocked to see the transcriptions in Google Translate of /’dəb(ə)l/ and /’wəndər/, when these transcriptions clearly should be /’dʌb(ə)l/ and /’wʌndər/, as the two vowels in those words are not the same for speakers (I daresay) of any dialect of English.
The vowel in the first syllable of both words is an actual realised vowel, like any other in the IPA chart. Individual idiolects will vary; but they tend to vary around a centre point of /ʌ/ (with, as Lindsey notes, some Northern English dialects using /ʊ/).
Whereas, in the second syllable of those words, the vowel is a neutral placeholder. In “double”, it is barely articulated (which is accounted for by the parentheses). This neutralness is the essense of the schwa.
In rhotic American English dialects, as well as in rhotic Scottish English dialects, an unstressed vowel should be in parentheses in conjunction with a final-syllable R just as it is in conjunction with a final-syllable L. In my own non-rhotic dialect of American English (I am a New Yorker), there is only the schwa at the end of a word spelt with -er, and no R. In non-rhotic British English dialects, the schwa before the R at the end of a word spelt with -er can resemble something of an /a/ or an /ɛ/ (depending on the degree of poshness), with no R.
The important point here is that in none of these cases is the second vowel in such a word a /ʌ/. It is a schwa, a different animal altogether, one that is characterised by its being in an unstressed syllable. Moreover, the use of /ə/ in a one-syllable word is entirely nonsensical.
So, notwithstanding Lindsey’s considerable charm, I shall stick with the sensible advice on the question of schwa that has long been given by many authorities.
Thanks for your interesting comment, Ferdinand. I’m not especially knowledgeable about phonetics or phonology, but I found Geoff Lindsey’s case to be quite persuasive. It’s certainly an interesting (and entertaining) debate to follow from the sidelines.
Maybe spectrographic analysis could shed light on the crux of the matter: the nature of the difference between /ʌ/ and /ə/. I expect Lindsey has investigated this. His earlier video reassessing the IPA is germane here too: