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In everyday spoken language when you, as native English speakers, say "glass" and "cup" are they considered as a synonym for you or you have a special meaning for each one of them?

As a non native English speaker I don't find a difference between

"I would like to have a glass of water."

or

"I would like to have a cup of water."

Then my question is:

Is the name of the vessel - in the spoken language - determined by the beverages which is going to be inside (e.g. cold and hot, alcoholic and non alcoholic), or by its shape (e.g. tall or short, flat or deep), or by the size of the capacity (e.g. 6-12 oz or more) or by the material which it is made of (i.e. glass for glass only rather than for porcelain, plastic, paper cups etc.)?

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    This is one of those things that makes a good category membership test — such as in studies where subjects rank birds according to how "typical" they are. (Penguins tend to lose out.) In other words, take a wide range of drinking vessels and ask people which ones are typical cups, glasses, and even mugs, and find out where they all land. :) I say this because I was shocked to learn recently that what I call a "mug" (meaning any cup with a handle intended for hot drinks) my mom calls a "cup", reserving "mug" for only the larger specimens of the category.
    – Luke Sawczak
    Jun 15, 2017 at 1:32
  • Also asked at EL&U: What's the difference between “cup” and “glass”?
    – choster
    Jun 15, 2017 at 4:38
  • Another related one from EL&U: Is “plastic glass” as a container a valid expression?
    – Chris H
    Jun 15, 2017 at 8:51
  • @fixer1234 these picture beg to differ. I'm sometimes asked "what sort of glass, straight or with a handle?" when buying beer (ale/bitter) in a pub. They are also known as mugs, so mug in this case can be a subset of glass.
    – Chris H
    Jun 15, 2017 at 8:54

6 Answers 6

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To throw in one more perspective (not to dismiss the other answers in any way), I think there is indeed wide variation and heavy overlap for these words. However, "cup" is probably more versatile.

The OED definitions overlap significantly

Here are the relevant Oxford English Dictionary definitions of "glass":

glass, n.1
II. Something made of glass.
4. a.  A glass vessel or receptacle. Also, the contents of the vessel.
5. spec. A drinking-vessel made of glass; hence, the liquor contained, and (fig.) drink.

But it supplies this telling note:

The specific application as in sense 5 is now so predominant that the word is now commonly applied only to vessels more or less resembling a drinking glass [...]

Meanwhile, here is the relevant definition of "cup":

cup, n.
I. A drinking-vessel, or something resembling it.
1. A small open vessel for liquids, usually of hemispherical or hemi-spheroidal shape, with or without a handle; a drinking-vessel. The common form of cup (e.g. a tea-cup or coffee-cup) has no stem; but the larger and more ornamental forms (e.g. a wine-cup or chalice) may have a stem and foot, as also a lid or cover [...]

One definition further down includes the wonderful "applied to various cup-shaped contrivances".

I think these entries serve to show us just how variable these words are: On the one hand "glass" is applied to "vessels more or less resembling a drinking glass", and on the other hand "cup" is applied to "a drinking-vessel, or something resembling it"! If you were to draw a Venn diagram of these definitions, there would be significant overlap of things that qualify.

However, if one were to be the broader category, it would seem to be "cup", which the OED only qualifies as "for liquids", whereas it takes the time to mention the material of a "glass". (But note that using the material as the main factor does not agree with several users' intuitions!)

Asking for a glass of water

Another of the definitions for "cup" is "drink; that which one drinks", not unlike "contents of the vessel" for "glass".

This suggests that both terms are also easily connected not with the object itself but with what's contained in it (synecdoche). Hence, a "glass of water" and a "cup of water", besides the literal meanings "a glass that is full of water" and a "cup that is full of water", could indeed be taken to refer to the same thing instead: the water that one would put in a cup or glass.

If you're wondering what's better to use in the request "I would like a ____ of water," I'd say it depends most on the establishment. At my local coffee shop, I ask for a "cup of water" knowing that all beverages are in plastic or paper cups, but I would get it in one of those even if I asked for a glass. At a sit-down restaurant, I'd ask for a "glass of water", but again I'd receive a glass vessel even if I asked for a cup. In a friend's home I'd ask for a glass by default, and could receive either vessel.

Note that for whatever reason, "glass of water" is far and away the more common collocation on Google Ngrams (source).

"glass of water" vs. "cup of water" on Google Ngrams

Whether this is because the phrase has just become fixed or because water tends to be served in glasses I don't know.

What these words mean to different people

However (and this is one pitfall of any dictionary), the fact that these words can apply to an object doesn't mean that they are typical of an object. What's worse, everyone will have a slightly different understanding of what that most typical specimen is.

There's a good type of study for this sort of question, though it's not exactly a lexicographical one so much as it is a psycholinguistic or semantic mapping one. The design is simple. You ask a bunch of people to rank various specimens of a type according to how "typical" they are of that type. You might show them a circle where the centre represents the ideal specimen and the outer edges are for unusual specimens and let them place the objects on that diagram. Then you take the average response and use that to determine what the key qualities of that type are.

For example, with birds, penguins tend to be placed on the outer edge, and red-breasted robins in dead centre. If we look at enough specimens we might conclude that what most people think of when they think of a bird is a small singing bird capable of flight that digs worms out of the ground, builds nests out of twigs, and migrates for the winter. Of course, in places where robins are less common than, say, parrots, the parrot's qualities will tend to define people's idea of an ideal bird.

I don't know if such a study has been carried out on cups, glasses, and other vessels such as mugs, steins, and tumblers. But it would be very interesting for your question to see how they're classified by people of different generations and geographical locations. But it wouldn't settle any arguments. ;)

For example, just reading over this thread, we see that according to various people the key qualities, the vectors by which we categorize these things, are widely in dispute!

  • The height and thinness are the determining factors, but also transparency and whether the vessel is used to hold liquor (@LawrenceC)

  • The intersection of the material and whether it has a handle determines the name (@fixer1234)

  • The material is "technically" the determining factor (@EDevinVanderMeulenII)

  • It seems to be dependent on the beverage the vessel is intended for (@JimMacKenzie)

  • Material, shape, and quality as a heat insulator are all factors (@Peter)

  • One category is a hypernym of the other; all glasses are technically cups (@cjl750)

Hence, we're not going to find one definition that suits everyone, even in one region, even in one family (I disagree with my parents over the things these words apply to). It's very much a matter of subtle associations. I suspect that the more everyday categories (cups, chairs, birds, rooms, animals, professions) are all highly subject to variation by individual discretion.

At the end of the day, if you're not confident about your own judgement, use what people around you are using. Also, questions like this make for fun topics in groups of linguistically inclined people: "Hey, would you call this a 'cup' or a 'glass'?" Then watch the feathers fly. :)

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    On "glass of water" vs "cup of water": people often argue about how many glasses of water one should drink in a day, but rarely how many cups of water (and those probably use cup to mean the unit of measure). At least in recent times that may explain the preference for that phrase.
    – Jeffrey Bosboom
    Jun 15, 2017 at 5:47
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    For another difference, take the OED's definition of cup, which it qualifies as "for liquids"". In the US, a "cup" is a measure of all sorts of things like flour, sugar &c used in cooking. And a "wine cup" is a kind of wild flower, while a stemmed glass typically used for wine is a "goblet".
    – jamesqf
    Jun 15, 2017 at 17:41
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    @JeffreyBosboom Yes, I think trying to avoid confusion with "cup" (a measured 8-ounce portion) is a major factor for why we don't use "cups of water" as often as "glasses of water". If someone mentions "2 cups of coffee", only context can tell you whether they filled their (arbitrarily sized) mug twice, or whether they mean 16 measured ounces, for a recipe or something.
    – BradC
    Jun 15, 2017 at 18:35
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    @J.R.: But a snifter is typically used for brandy, no? Only an absolute parvenu would use one for wine :-)
    – jamesqf
    Jun 16, 2017 at 5:49
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    @BradC: Which brings up one of my pet peeves, the makers of coffee machines who label them in "cups" that are half the size of a legal cup, or the cups normal people use to drink coffee. (Well, OK, me and my acquaintances, whether we qualify as "normal" is another question :-))
    – jamesqf
    Jun 16, 2017 at 5:52
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This is an excellent question!

As a native English speaker I agree with your guess at the end of your posted question. Although functionally the two words are used interchangeably in speaking, technically a "glass" can only be a drinking container made from glass material. Although a native speaker usually would be rather lazy with the use of these two words, it does sound slightly odd to call something made from plastic or wood a "glass".

Please see:

cup 1 A small bowl-shaped container for drinking from, typically having a handle. Oxford Dictionaries

glass 2 A drinking container made from glass. Oxford Dictionaries

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  • To paraphrase then (in theory), all glasses are cups, but not all cups are glasses. This is personally how I have come to use the words as an adult.
    – cjl750
    Jun 15, 2017 at 2:30
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    As a native British-English speaker: no, they are not used interchangeably. A glass is a drinking container made of a transparent material (we have picnic glasses made of plastic) for cold liquids. A cup is a drinking container made of an opaque, non-glass, material for hot liquids. (Exception: you might give milk to a child in a cup because cups are more robust.)
    – Martin Bonner supports Monica
    Jun 15, 2017 at 8:04
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    Agree with @MartinBonner. There can be overlap, but usually there isn't in normal use (BrE).
    – TripeHound
    Jun 15, 2017 at 10:31
  • @cjl750, Not necessarily true. I called a glass a cup in front of my parents a few weeks ago, and I had to clarify it to glass when they weren't sure what I was talking about. To them, a glass is never a cup and is always made of glass. Could be regional, could be generational.
    – Karen
    Jun 15, 2017 at 17:02
  • @Karen I suspect it is both regional and also just varies from person to person. So what I say isn't likely what others say. Jim's answer makes this clear. I'm just paraphrasing what this answer says (at least as far as I interpret it): "the two words are used interchangeably in speaking, [but] technically a "glass" can only be... made from glass"
    – cjl750
    Jun 15, 2017 at 17:28
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The determining factor between glass and cup is height and or thinness.

A glass is typically made of glass and is tall. It's possible a container made of clear or translucent plastic that's a similar shape could be called a glass if it's made for drinking.

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A cup may not be made of glass, and is shorter, wider, flatter.

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A vessel that fulfills the height/thinness criteria for a cup, and is still made of glass, can be called a glass cup.

Except teacup - those may be made of glass but you never say "tea glass."

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However, anything designed to hold liquor that is made of glass is generally called a glass (except a bottle of beer) regardless of height. Esp. a shot glass, wine glass, or bourbon glass, e.g. versus (plastic) red solo cup.

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    At least in my part of the US, another defining factor is that a glass is almost always transparent or semi-transparent, even if it's made of plastic. But an opaque plastic vessel the same size & shape as a plastic glass would likely be called a cup.
    – jamesqf
    Jun 15, 2017 at 5:51
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I think this is very regional. Here in prairie Canada, you would most likely call a plastic cup of water a "glass", and a glass mug of tea a "cup". It isn't entirely logical; it seems dependent on the beverage.

I would never ask for a cup of water, but rather a glass. I would always ask for a cup of tea (but a glass of iced tea). I think that if a person aspires to sound fully fluent, one will just have to pay attention to the English dialect where they most often speak English.

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Often the material and shape is what matters in making the difference between a glass and a cup.

Glasses tend to be larger than cups since they are used with colder fluids and made of, well, glass, which is a very efficient heat conductor. One of the reasons for long stems in wine glasses.

Cups tend to be made of ceramics which are good heat insulators and often hot beverages are served in cups or mugs.

You will be able to find examples of glass cups or mugs but you will not be able to find examples ceramic glasses.

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Just a personal data point, from a native of Kansas City, which has a dialect said to be used by newscasters in the US.

Any HOT beverage would need a container with a handle, which I'd call a cup. Cup of coffee, cup of tea, cup of hot chocolate.

Any COOL/COLD beverage that you could hold a container of beverage of would by default be served in a glass. Glass of water, glass of ice tea, glass of soda, glass of beer.

I would only ask for a mug of something if I somehow knew mugs were available and being considered for use: a vendor is handing out mugs of beer, or your hostess actually brings mugs out with a pot of hot chocolate or something. If your hostess had mugs clearly visible on the counter, but had brought out coffee cups along with the hot chocolate, or in any other case where the mug wouldn't be what the server is going to use by default, I'd be asking for a cup of hot chocolate. By the same logic I'd ask for a cup of soup if the server had cups at the ready, otherwise a bowl of soup.

Whether you specify a cup, glass, or mug, this is just a manner of speech and doesn't indicate you'd be surprised or even notice if you got a different container.

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