Prompted by the title of this question and a couple of comments on it, I'm minded to think there that many "states of being" that you can be "on", as in...

on fire, on holiday, on guard, on the blink (intermittently faulty), etc.

Sometimes we just use [verb]ing to generate an appropriate word (holidaying, guarding, resting, etc.)

Or different prepositions (in purdah, at play, under suspicion, etc.)

Is there a (even partially-applied) rule indicating when on should be used?

Just to muddy the waters a bit (or maybe it'll inspire someone to see the rule, I dunno). You're at lunch, but on your lunch-break.

By way of one final 'tickle', I wonder if the difference between in retreat and on retreat will spark a line of thinking in someone ("in..." meaning "running away", whereas "on..." probably implies you're spending some time at a monastery or similar).

  • Why rules for everything? rules make things complicated.
    – user8568
    Commented May 26, 2011 at 19:35
  • @Explorer: The thing is few of us would disagree with the idiomatic assignments rajah9 so laboriously provides below. We probably haven't all learnt this list like you'd have to if it were a list of telephone numbers, for example. Almost certainly the choice of which preposition to use largely follows a small number of not-conciously-recognised rules. It's just that we don't seem able to "reverse-engineer" those rules. Commented Sep 22, 2011 at 17:45
  • Yes you're right.
    – user8568
    Commented Sep 22, 2011 at 21:44

4 Answers 4


I really don't think that there is a rule. and if there is one, I've never heard of it. These are all idiomatic expressions, which by definition have a meaning which isn't derived from the meaning of their components.

  • @JSBangs: I'll buy on the blink as idiomatic, but the rest aren't, in my view. The only odd thing about them is that we (you & I, at least) don't conciously know a rule for which preposition to use. Commented May 26, 2011 at 19:49
  • @Fumble, I eagerly await someone coming and specifying the rule, then, so that I can upvote him. Commented May 26, 2011 at 19:50
  • @JSBangs: What gets me is I can't correlate it to anything obvious like time (it's neither old, nor new), or semantics, or the way the 'on' words can be used in other contexts. But for any given word, I don''t seem to have any doubt about the 'correct' form. Maybe it's just that for any given word I've heard the correct usage before, so I just 'know' that's right. Commented May 26, 2011 at 19:58
  • 1
    @Fumble, your certainty isn't an argument for it being non-idiomatic, since of course you also know exactly how idioms should go, right? But the lack of any evident semantic or syntactic constraint strongly suggest that these are simply unpredictable idioms. Commented May 26, 2011 at 20:11
  • 1
    @FumbleFingers: My definition of idiomatic: that which is irregular but received—as opposed to either solecisms or usage that follows a rule. Unidiomatic is that which is counter to idiom, and therefore "wrong". Commented May 27, 2011 at 4:26

I came up with some various states of being that we use with prepositions. I then alphabetized them to group them by preposition. Since the linguistic rules are usually encoded in our brains and not written down, linguists have to infer what the encoded rules might be.

  • awake
  • asleep
  • at a party
  • at attention
  • at ease
  • at my desk
  • at play
  • at the point of no return
  • at work
  • in a jam
  • in a pickle
  • in line ("on line" in New York and UK)
  • off duty
  • off the grid
  • on a roll *
  • on break *
  • on drugs
  • on fire *
  • on guard
  • on tip toes / on his toes *
  • on line ("in line" when not in New York or the UK)
  • on pins and needles *
  • on the blink *
  • on the fritz *
  • on the house ("free") *
  • on the pill
  • on time *
  • on track
  • on vacation *
  • online (electronically attached)

Some of the "on" prepositions seem to fall into a category of the contrast of on/off. Consider:

  • on duty / off duty
  • on guard / off guard
  • on track / off track
  • on grid / off grid
  • on drugs / off drugs
  • on the pill / off the pill
  • online / offline

(I have starred the "on" states of being from the first list that do not fall into an on/off category.)

But why not on the blink / off the blink? These idioms are probably too hard to reverse ("off the blink" would mean "working consistently"). Why not on fire / off fire? Perhaps because "on fire" or "afire" are already linguistically indicated: it is an unusual state for something to be on fire. Note that if it is the normal state for something to be on fire, we don't use the phrase "on fire," we use "on" or "lit." (For example, you don't say that the stove is "on fire" if someone left a burner on. When you say, "The stove is on fire," you would probably need to call the fire department and evacuate the house.)

Same reasoning for on vacation / off vacation. "On vacation" is the indicated form, because "at work" is where we are for 90% of the time.

I would propose the "on" rule as:

Use "on" when the state-of-being implies that the subject is following a normal course of action.

So for the second list,

  • on duty = I am in the state of working
  • on guard = I am in the state of guarding
  • on track = I am in the act of tracking
  • on grid (No, this one doesn't work, perhaps because "on grid" is the less-indicated state)
  • on drugs = I am following the course of taking medications
  • on the pill = (same)
  • online / offline = I am in the act of communicating with an electronic device

The other starred items (e.g., "on his toes," "on the fritz") have a very idiomatic feel to them, at least to my ear.

I could use some help in improving the rule, which I am sure the SO community will be willing to provide.

  • It does look like a good start. We certainly seem to use "on" where it's reasonable to use "off" for not being in that state, but I don't see this implies the "on" version is the "normal" state. I won't get too hung up over The house is off fire, because that one may just be an idiomatic exception. Commented Jul 26, 2011 at 18:38
  • @FumbleFingers, (hand waving start) "on fire" is unusual, so there is no corresponding "off fire." "On tip toes" is unusual, so there is no corresponding "off tip toes." "On pins and needles" is unusual (and suspenseful), so there is no corresponding "off pins and needles." Maybe on/off works for list two because they contrast nicely and the on condition is a normal course of affairs. But on/off doesn't work for the starred in list one because the "on" state is unusual. (hand waving end)
    – rajah9
    Commented Jul 26, 2011 at 20:55

I know this answer might be a bit late, but:

Basically, the subject has to have been modified to it to achieve the state of being it's in. For example: The house was set on fire, so now it's on fire. The man stopped working, so now he is at rest.

Sometimes, as another answer mentioned, some of these "on" or "at" states may be idiomatic expressions, so there may be exceptions to the rule.

The reason some verbs cannot be used with on (for example, dance) is because "on dance" is not a state of being. The subject is not being modified.

Edit: I realized that I left a few things out in my answer. Here we go:

Something I forgot to mention is that the "on" is sort of like a switch. You can either be on vacation or not on vacation. It's the same thing with "on fire." The house is either on fire or it's not on fire. There is no in between. When I say the subject is being "modified," it means the switch is being turned on or off.

Anything that falls under the category of "What are you actively doing right now?" (such as dancing) does not have an "on" before it. This is because there are many possibilities as to things you could actively be doing now. Meanwhile, in our house fire, we only have 2 possibilities.

Any exceptions to this rule are usually idioms.

Hopefully that clears things up a bit.

  • It's not obvious to me that holiday, guard, vacation, etc. share with fire much along the lines of the subject having been modified to achieve that state. It's true you can be put on guard, or sent on vacation, but that seems to be just because those 'activities/states' are the ones that take "on", the same as fire. Commented Jul 25, 2011 at 2:30

Newton's Law of Motion states that an object at rest will tend to stay at rest, and an object in motion will tend to remain in motion.

First, there is a group of words that are formed by taking verbs and adding "ing" to them, which transforms them into nouns. Specifically, it tranforms actions into "states of being," resting, partying, etc. These are known as gerunds.

In other instances, words are in states of being when used with one PREPOSITION, and in states of motion when used with another one.

Example: "Retreat" means "withdrawal." Therefore "ON retreat" implies a Planned withdrawal, or state of BEING, perhaps at a resort. "IN retreat" implies an UNPLANNED withdrawal, from a lost battle, or an ACTION.

Another example: "The house is on fire." The emphasis is on the state of the HOUSE, which is in the state of undergoing fire, vs. "The fire is on the house," as in "The drinks are on the house." (The house will give out FIRE.) Here, the word order shifts the emphasis.

  • Did I miss something? Why exactly does on retreat imply a planned action, and in retreat an unplanned one? How do we 'know' that? Commented Jul 26, 2011 at 18:32
  • If you are "on" or "onto" or "on top of" something, you are (usually) following your own agenda, and if you are "in" (or "inside") something, you are being forced to follow the lead of someone of something else. As in, if I'm IN your home, I'm attending your party and enjoying drinks and entertainment provided by YOU.
    – Tom Au
    Commented Jul 26, 2011 at 19:21

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