Because the trail of comments under the question was effectively long, they have been transferred to chat where (probably) no one will ever read or see them again. So in order of appearance, I'll cite the comments which I believe were the most thought-provoking. Apologies to any whose comment/s are not included.
Comments
Behind the witty and nerdy comment lies a more serious observation: because toast is made from bread, which is a mass noun, it is therefore a piece of that solid mass form. For the benefit of future visitors, a link to the law of conservation of mass.
- Because of the law of conservation of mass nouns, which states that no matter how much energy you apply to a mass noun, you can't change it into a countable noun, only into another mass noun. Thus bread is a mass noun, and if you apply heat to it you convert it into toast, which by the law, remains a mass noun.
• deadrat (ca.60 upvotes)
- Bread is bread, no matter how you slice it. The energy applied to the knife in slicing a loaf of bread won't change the bread into a countable noun.
• deadrat
Yet, there are instances when a mass noun can be either ‘countable’ or ‘uncountable’ depending on the context and its meaning.
- Grain has both countable and noncountable uses. The former because there are different types of grain: "This field is planted in a grain; that one, in a legume." But although we have been given pictures of different types of toast, it's still a mass noun only. @Mari-LouA, can you add a picture of French toast?
•deadrat
An American user who sustains that nowadays it is common to hear toast used in its countable form
- Hate to break it to you, but it's not at all uncommon to hear "two toasts" in the US. And sometimes that's even while having breakfast.
• Hot Licks
I'm not quite sure what skymnigen's point was, perhaps someone could shed some light.
- If toast was countable, what would we be counting? The slices of toast or the loafs of toast?
•skymningen
The comment which immediately follows; however, illustrates how it is possible to ‘count’ toast in a native-like manner. I found this comment to be very natural-sounding.
- All I know is that after the 3rd or 4th toast I lose count.
• Hot licks
Another user pointing out that mass/uncountable nouns such as meat can be ‘counted’, especially when one is ordering from a restaurant menu. Although the user is arguing that meat shouldn't be reclassified as being countable, the example does show how native speakers will adapt language to fit their needs.
- If I'm in a restaurant with my family and ordering Sunday lunch, I'm likely to say "That will be 2 beefs, 2 lambs and 1 pork please". But that doesn't mean that "beef", "lamb" and "pork" should be reclassified as countable nouns.
•Bill Johnstone
A user who sustains that the term toast is just the clipped form for “toasted bread”
- I mean, isn't "toasted bread " as uncountable as "bread" is? A toast is just short for "a sandwich prepared with toasted bread" in the same way as "a water" can be short for "a bottle of water".
•Josh61
A bubbly comment that reminds us toast is both a noun (a toast to Alice!) and a verb, (let's toast to world peace) meaning to raise a glass of champagne (or any appropriate drink) in honour of something or to one or more people. In this case, toast is certainly countable. In Italian it is called brindisi, which happens to be the name of an important coastal town in the south of Italy.
- A toast to this question! And I call for more toasts so that we can count them!
• CJ Dennis
Sometimes there is no explanation, it's just the way things are...
You know, sometimes the answer (especially in this forum) is "It is what it is." There is no "logic" to many things in English. It is largely the result of Brownian motion and, were the clock somehow wound back and it done all over again, many things would be completely different.
• Daniel R Hicks (Hot Licks)
The history of how 'toast' is uncountable is followable (there are instances mentioned here where it is not, but most instances (in the expected meaning) are uncountable. 'Why' may be difficult to substantiate other than an explanation by analogy with other uncountable situations. It does seem weird since you'd think that pieces of toast should be called 'toast' plain and simple. Why it is not is I think just 'because'.
• Mitch
Edwin Ashcroft argues the need for a more thorough investigation as to why toast is considered uncountable
- Bill Johnstone Classifying nouns which exhibit both types of behaviour as either 'countable or 'mass/uncountable' is poor analysis. Its usages that are count or otherwise (or sometimes apparently halfway between: a gentle light suffused the scene / two gentle lights ...). // OED apparently labels toast 'countable'; I'd prefer separate entries (or at least 'noncount and count') under the same headword. Some dictionaries show this level of sophistication.
• Edwin Ashworth
At this point, someone recites The (Holy) Oxford English Dictionary
[…] 1838 Dickens Let. 1 Feb. (1965) I. 366 ‘We have had for breakfast, toasts, cakes, ...’ 1978 Vishveshvaranand Indological Jrnl. 16 218 ‘He had stopped taking cereals ... but ...had to re-start on medical advice taking two toasts or some cornflakes.’ The OED has two 'toasts'. The first (older) is 'put in wine, water, or other beverage' and is countable. This usage is rare or obsolete except in India. The uncountable usage is first recorded (OED) around 1735 - Swift Panegyrick on D— in Wks. II. 294 ‘Sweeten your Tea, and watch your Toast’. Also 1885 J. Ruskin Præterita I. iii. 84 ‘Quarrelling with her which should have the brownest bits of toast.’
• Dan
EdwinAshworth - OED gives two 'toasts' - the older, countable, used with drinks and now with strongly regional usage, and the more recent (1735), uncountable, current usage.
• Dan
Another citation from the OED which supports that toast is a mass noun.
- I wasn't implying otherwise Edwin; the point I was making was that we use the terms countable or uncountable for their predominant use, so I would not expect the "beef" in "Can I have 2 beefs and 1 pork please?" to be listed as a countable noun. If a noun can freely be used both ways, then dictionaries will cite both, though with some nouns consistency is patchy. For example, the basic Cambridge Online Dictionary gives "toast" (the food) only as uncountable, whereas the Oxford gives it as uncountable, except for "stilton and pear toasts" which it correctly says is countable.
• Bill Johnstone
A user from Europe who points out that toast is countable in French. The same is true in Italian.
- You may find the following interesting : TLFi with the reference to the Bath, Sommerset anecdote, and DmF for the tostee. In Fr this is countable (that I know of), will even take the mark of the plural (toasts), but should always be pronounced like the singular (toast/toste). It's all quite interesting. Thanks!
• Amphiteóth
A veteran EL&U memeber who argues the grammar supporting the non-countability of toast does not reflect modern usage, and provides evidence to support his claim.
I don't usually have many disagreements with Downing and Locke (English Grammar: A University Course' [2006]) but I think their 'Note that toast meaning 'toasted bread' is always non-count and requires 'a piece [etc] of' in order to refer to an individuated piece' is outdated (though reflected on many grammar sites and in several dictionaries). I'd say that countification (of the bread sense) (and according to Uri's update, that should be recountification) is progressing increasingly quickly today.
• Edwin Ashworth
I'd add to the previous comment that the other common type of countification process, to the 'varieties of' ('arabica and robusta coffees are the two most commonly used'; contrast 'two coffees to go, please'), is clearly in use: {laweekly.com} '10 Best Classic French Toasts in Los Angeles'. This article also contains the noncount usage, and, arguably, the slice-count usage.
Responding to my comment that posited pancakes were countable even though the substance, batter, was uncountable. (Remember deadrat's first comment)
- Mari-Lou A: Counting pancakes: You can count pancakes because the batter has been quantized. This is elementary quantum mechanics.
• ab2