• then, press the button of heat.

I extracted this sentence from my own paragraph.

My teacher told me that I cannot use “the button of heat”; instead, she told me to write it this way:

  • Then, press the heat button.

My question is why can’t we use the first version with “the button of heat” or “the switch of light”?

Why should we say the “light switch or heat button”.

I learned that x of y is the same as y x.

So why cannot we apply this approach to my example?

  • 1
    Isn't this really a button that turns on the heat? In which case, it would be: the ON button.
    – Lambie
    Apr 9, 2018 at 15:14
  • 4
    While "the heat button" is the better of the two, it doesn't sound quite right to me. With a little more context an even better alternative might be found. Apr 9, 2018 at 15:25
  • 1
    @Lambie Maybe it's the "On button for the heat system", but "heat button" is shorter with the same meaning. Depending on the context (as in a car), there might be many buttons that turn different things "on". Apr 9, 2018 at 15:45
  • 1
    To add fuel to the fire: What about "hot button issues" -- metaphorically, issues like buttons, that, when pressed, turn up the heat. :)
    – Andrew
    Apr 9, 2018 at 15:53
  • 1
    "button of heat" implies a button made of heat.
    – Boann
    Apr 9, 2018 at 19:50

4 Answers 4


In some cases, it is true that X of Y is the same as y x, for example:

the face of an angel
an angel face

In other cases, both make sense but have different meanings:

a bottle of beer - refers to the contents, not the bottle
a beer bottle - refers to the bottle, not the contents

In your examples (heat button and light switch), the first noun describes the purpose of the second noun. If you look at the Cambridge Dictionary definition for of, there are many meanings but purpose is not one of them, so "button of heat* and "switch of light" don't make sense.

  • 2
    @Lambie: It depends on context... some things really do have a heat button.
    – psmears
    Apr 9, 2018 at 15:23
  • 1
    @Lambie: Not sure if you read the text for that link, but the button isn't for heating the seat!
    – psmears
    Apr 9, 2018 at 15:43
  • 1
    @Lambie: The button is not for the car heating system, either! There are a lot of posts calling it the "heat" button, which is natural because it's a button and it's labelled "heat". And besides, I think you possibly missed the other link I posted - in that case the phrase "heat button" is in the manufacturer's instructions.
    – psmears
    Apr 9, 2018 at 16:13
  • 2
    @Lambie: We could avoid some of the repetition if you could possibly read more carefully :) The first button is not for heating the seat. It doesn't heat the seat because that's not what it's for. It's not for the car heating system, either. So please can you stop talking about those things? They're not relevant. My point is that there are some things that genuinely are a "heat button" - like the one in the picture in the car post... Look carefully: about 80% of the way down from the top of the photo, about half way across - it clearly does say "HEAT" :-)
    – psmears
    Apr 9, 2018 at 16:27
  • 4
    Not to mention, even when "y x" means roughly the same thing as "x of y", it can sound grandiose to use "x of y". Consider "fire starter" with "starter of fire". One is just a tool to get a campfire going, while the other might be the title of some daemon who is the origin of all forest fires. Apr 9, 2018 at 18:17

As others have noted, the equivalence you're using for "of" works for composition, not for purpose. The comparable equivalence for purpose would be "for". "The hot water tap" = "The tap for hot water". Note that the tap isn't made of hot water, it provides it; the hot water is the purpose of the tap.

So in your example, you might use "the button for heat" or "the switch for light", however this last one is almost always idiomatically rendered as "light switch" when referring to light. "The switch for sound" would be equivalent to "the sound switch".


It's certainly not true that X of Y always means the same thing as Y X. That can be true in certain situations, but most definitely not all the time. Here's an example where it's true:

He is an employee of Microsoft.

He is a Microsoft employee.

One simple counterexample to show that the statement X of Y means the same thing as Y X is not true is that a bottle of beer does not mean the same thing as a beer bottle. The first example talks about a bottle that literally has beer in it (the actual liquid). In the second example, we're talking about a bottle that is used or has been used as a container to store beer as opposed to storing some other type of liquid such as milk or juice. For example, when you go outside and see a bunch of empty bottles scattered on the ground, you'd say that I see beer bottles lying on the ground. You would not say I see bottles of beer lying on the ground because that would imply that the bottles are still full of beer.

Now, let's get back to your "heat button" example. The phrase button of heat actually sounds like you have a button that's made of heat or contains heat, which is kind of nonsensical. The phrase heat button is fine because the word heat is used as an adjective describing the button. What kind of button? A heat button. A button that's probably used to regulate the amount of heat generated in or by some sort of device.

  • 2
    Slightly complicating this: "A bottle of wine" is a measure of how much I had to drink on Friday night. The wine's not in the bottle any more, and if the recycling's been collected, the "wine bottle" may not exist either. Apr 9, 2018 at 16:45
  • 1
    @Roger Lipscombe That's exactly right. When you swill down a bottle of beer, what you're left with is a beer bottle while the bottle of beer itself is gone. Apr 9, 2018 at 16:58

Generally, but not always, x of y means y's z, which may be different from y x.

The button of heat is not idiomatic English, and nor is heat's button.

A button of heat could mean a button made of heat. Which doesn't really make sense.

This is unlike some other languages in which a there is a "genitive" that can be used like this. Instead nouns can be used to form a compound nouns like "light switch" or "beer glass".

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