Is this a valid sentence?

I’m running into a ridiculous amount of people at Ala Moana.

I found it on Twitter, and I don’t know what Ala Moana is, but let’s press on all the same. My real question is whether amount of people is acceptable. Think about it, and while you’re thinking, let’s talk about count and mass nouns.

The distinction between count and mass nouns is a core feature of noun usage in English. It’s brought up in less academic contexts most commonly in rage against the express lanes of supermarkets, where the “15 items or less” sign generates incessant grumblings about how it needs to be “fewer”. (This is not a position I agree with.)

The distinction is simple to state, but not necessarily simple to enforce. There are count nouns, those that refer to distinct, countable, pluralizable objects. Count nouns are things like arc-welders, wallabies, prickly pears, or people. You can say things like I have forty-five arc-welders in my garage. Mass nouns, on the the other hand, are objects that are not really countable, that don’t come in quantum units, and generally don’t get pluralized. These include sand, tofu, air, and sulfuric acid. Abstract nouns are especially likely to be mass nouns; think of independence, prosperity, or music. You can’t say something like I have two prosperities in my garage. Pretty easy, right?

Well, the trouble is that countability isn’t as cut-and-dried as it seems. For instance, mass nouns can be converted to count nouns when certain pragmatic conditions are met. One way to do this is to specify a unit size, as in:

(1a) There’re four two-liters of Mountain Dew in the garage.
(1b) Greg managed to get a single grain of sand under his fingernail.

Something that I find neat is that mass-to-count conversion can happen as a zero-transform, a conversion that is not explicitly marked. This happens when the mass noun has a pragmatically salient unit division. You’re probably familiar with this in restaurants; I went out with some friends the other night, and three of them ordered Diet Cokes. When the waiter returned to our table, he said

(2) Okay, three Diet Cokes.

To which my one friend responded

(3) I’ve got one.

In this situation, there is a pragmatic quantum of Diet Coke, the refillable glass delivered by the waiter. (I don’t think in my wildest daydreams I ever believed I would ever write the phrase “pragmatic quantum”, but there it is.) Because this quantum is salient to everyone involved, there’s no need for an explicit converter like “three glasses of Diet Coke”.

Conversions from count to mass are possible as well, but they’re a little more subtle. Mass-to-count conversions arise when separating a mass; the count-to-mass conversion arise when aggregating something separable. You can tell when these conversions are being made because fewer won’t sound right. (Normally, fewer is used with count nouns and less with mass nouns.) Consider these two sentences:

(4a) There’re four less/fewer dollars in my wallet than I expected.
(4b) The pants were four dollars less/?fewer than I expected.

In (4a), I would use either less or fewer, with a slight preference perhaps for fewer because I’m thinking of the dollars as individual bills. In (4b), I would solidly prefer less, because the cost is an aggregated amount. The count noun dollars is converted into something more mass-like. But note that the conversion isn’t complete; the dollars remain countable as well. This is the same thing that’s happening with 15 items or less; the grocery objects are being thought of as a mass, even though they still look count-y.

[Bunches of bananas]

Five bananas in a single bunch would be considered a single 'item', a subtle count-to-mass-to-count transformation.

All of that in mind, let’s look at the Twitter sentence again. It was (5a), but should it be (5b)?

(5a) I’m running into a ridiculous amount of people at Ala Moana.
(5b) I’m running into a ridiculous number of people at Ala Moana.

In general, the rule is that number of goes with count nouns and amount of goes with mass nouns:

(6a) I’m drinking a large (amount of|*number of) milk as part of a bet.
(6b) I’ve run afoul of a large (?amount of|number of) rules today.

So that suggests that (5b) is the better choice. But if you’re like me, you’ll find an asymmetry in (6). Number of is straight ungrammatical in (6a), but amount of is at worst awkward or non-standard or informal in (6b). That’s because count nouns can be thought of as in aggregate more easily than mass nouns can be thought of as individuals. Going back to (4b), when we think of normally-count nouns as an aggregate, they can take on mass nouns agreement — by which I mean the use of less rather than fewer, much rather than many, and amount of rather than number of.

In fact, there are instances where one may want to choose between amount of and number of in order to push the audience toward the more or less aggregated interpretation. Consider this sentence from a 1940 book, quoted in the Merriam-Webster Dictionary of English Usage (MWDEU):

(7a) […] we could absorb a vast amount of South American products.
(7b) […] we could absorb a vast number of South American products.

The aggregated usage in (7a) suggests that we are talking about how much South American production (of any number of goods) can be absorbed. The counting usage in (7b) suggests we’re talking about the number of types of South American products that can be absorbed. A specific version of (7a) might read absorb 7,000 pounds of SA products; for (7b), it might be absorb coffee, cattle, and cacao.*

Furthermore, the use of amount of with count nouns is well-established throughout the last 200 years. The OED’s first example is from 1801: “A number of little birds, to the amount I believe of twelve or fourteen.” (Amount as a noun only dates back to 1710, by the way.) The MWDEU notes that it’s only in the last hundred years or so that anyone complained about amount of with count nouns; it also notes that the condemnation begs the question. The basis for the argument that amount of is inappropriate for count nouns is nothing more than stating that it’s inappropriate with count nouns, and that’s clearly not true, given examples like (7a). Amount of is certainly awkward when the count noun isn’t aggregated (*the amount of parents I have is two), but it’s fine, or sometimes even preferable, when the count nouns are aggregated.

So in the end, is amount of people okay? Well, yes, especially if you’re thinking of the people as a teeming mass of humanity (a count-to-mass transformation), or a bunch of undifferentiated people getting in the way (an aggregation) when you’re visiting the largest open-air shopping center in the world (I finally looked up what Ala Moana is).

Summary: Amount of with a count noun is at worst a bit informal, and there’s nothing inherently wrong with using them together. The combination is useful for suggesting that the pluralized count noun is best thought of as a mass or aggregation, so you ought to let yourself use it when it’s useful.

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*: (7a) was the original, if you were curious. (7b) is concocted.