As we were chatting at a summer party last weekend, someone brought up the possible minimal pair archaic vs our cake. We were trying to think of a context in which there might be a plausible confusion between the two. Finally someone came up with a scenario involving two daughters visiting their elderly mother. They brought with them a cake as a gift, which their mother promptly stored in a tin. But she had numerous cake tins, all looking much the same, and tended to accumulate old cakes or pieces of cake and keep them in the tins for months. When it’s time for tea, one of the daughters looks at all the cake tins, picks one, and asks her mother “Is this one archaic/our cake?”
Non-native speakers may be surprised that this is even considered a minimal pair. Surely aʊə ˈkeɪk is rather different from ɑːˈkeɪɪk. Well, yes, if that’s what you say. But if you are one of the many NSs who pronounce our as ɑː(r) (rather than as aʊə(r)), then the difference is only a matter of the vocalic material between the two velar plosives, keɪk vs keɪɪk, which comes down to a subtle question of timing.
There are two reasons why our might be monophthongal ɑː(r). It might be through the operation of the optional process of smoothing, which deletes the second part of the diphthong aʊ when followed by another vowel [and, I should have added, compression, which makes two syllables one]. This is what gives us RP pɑː power, ˈɡɑː striːt Gower St, etc. (The quality of the resultant monophthong may or may not be identical to that of the ordinary ɑː of START words.)
But it might also be simply that ɑː is the default pronunciation of our. Not everyone has our as a homophone of hour. That is true for me, and for an unknown number of other NSs. The two words make a possible minimal pair, ɑː our vs ˈaʊə hour. And ɑː is not just a weak form: it’s the strong form too. (I ought to do a preference survey for this.)
When I was taught the Lord’s prayer as a child, it began ˈɑː ˈfɑːðə, hu ˈɑːt ɪn ˈhevn̩.
I might ask you “Did your bus come on time? We had to wait for ˈa(ʊ)əz for ˈɑːz.”
I don’t think there are many NNSs who pronounce our, ours as ɑː(r), ɑː(r)z. On the other hand there may well even be a majority of NSs who do. No one knows.
Kenyon & Knott included ɑr as a possibility for AmE as long ago as 1953 (possibly even in 1944 — I haven’t got the first edition to hand). For BrE priority goes, I think, to Jack Windsor Lewis, in whose Concise Pronouncing Dictionary (1972) ɑː is included just as a weak form.
When still edited by Daniel Jones, EPD did not recognize the ɑː variant. It was only when Gimson and Ramsaran took over that it was acknowledged as a possibility. Now the OED, too, has caught up.