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  1. Symptoms will develop within five to six days after contracting the disease.
  2. Symptoms will develop within six days after contracting the disease.

What is the difference between (1) and (2)? They both mean before six days have passed, don't they?

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    The writer wasn't thinking. Logically, it should be "five or six days after" or "within six days of". Commented Mar 4 at 9:23
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    The former suggests typically it will take 5 or 6 days and no longer, but it's not very precise so doesn't seem good for medical purposes.
    – Stuart F
    Commented Mar 4 at 10:09
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    No one is asking, so I will. Please supply the source of the quotes, or tell us whether you invented the two sentences yourself. It seem unlikely that anyone would write "within 5 to six days" when the maximum limit is six days. I could understand the indications "within 7 OR 10 days" Meaning the infected person could get sick any day between day 7 and day 10.
    – Mari-Lou A
    Commented Mar 4 at 17:36
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    You see this kind of imprecision a lot. You probably ignore it when it happens in your native language. Compare the expression "up to 15% or more off!" OB xkcd
    – James K
    Commented Mar 4 at 19:06
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    If I were told "within five to six days", and developed symptoms after seven days, I would not be at all surprised. If I were told "within six days", and I developed symptoms after seven days, I would be a little bit surprised. So to me, I think the difference is that one expresses more certainty than the other. But this is just one data point, so perhaps not worth an answer. Commented Mar 5 at 0:58

7 Answers 7

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The difference is that "within 6 days" is a clear and logical statement which means "at some point in time between now and 6 days from now", while "within 5 to 6 days" is an ambiguous statement with no single clear definition: it could be a sloppy way of saying "within 6 days", or it could be trying to convey "between 5 and 6 days after", or it could even be a sloppy way of saying "within 5 days". Unless you can read the author's mind, you can't know which meaning was intended.

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    exactly correct
    – Fattie
    Commented Mar 5 at 13:30
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    I will see you within 5 or 6 days. means from between day one to day six. A time period of five or six days begins on day 1. Saying it is clear and logical does not explain what it means. -1
    – Lambie
    Commented Mar 5 at 18:19
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    @Lambie: eh? I did not say that "within 5 or 6 days" is clear and logical, because it is anything but. If you mean "I'll see you sometime in the next six days", then what is the 5 doing in there? Why not "within 3 or 6 days"? Ah, but then it needs to be "within 3 to 6 days", and it becomes increasingly obvious that "within" is the wrong word to be using.
    – Martha
    Commented Mar 5 at 22:08
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    "within 6 days" is a clear and logical statement, You did say that.
    – Lambie
    Commented Mar 5 at 23:14
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    I agree that sentence (1) is fundamentally ambiguous. I would personally be inclined to interpret it as something along the lines of "within 6 days, but probably closer to 5 than to 1", but I would not be prepared to argue for that as the way it necessarily should be interpreted. Commented Mar 6 at 21:53
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In direct answer to your question, yes - they both mean before six days have passed. However, there is a clear difference.

Cambridge defines 'within' this way:

inside or not further than an area or period of time:

So, it can mean two things - inside two given points, or no further than a single given point.

  • "Within 6 days" implies that the symptoms could begin at any point before the 6th day - on day 1, day 2, day 3 etc
  • "Within 5-6 days" is a more specific time frame using two points of reference. It means that the symptoms will most likely occur on day 5 or 6 following infection.
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    @Lambie Is that evidence-based?
    – Astralbee
    Commented Mar 4 at 16:39
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    @Lambie yes mine is based on the dictionary definition which makes it very clear 'within' can be used to indicate a limit or a range. One point indicates a limit; two would indicate a range.
    – Astralbee
    Commented Mar 4 at 16:48
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    I think the language is somewhat imprecise here. If you really wanted the lower bound, you could say "within between five and six days after infection", which is obviously clunky, but I don't think "within" can have a definite lower bound without it. Given that it's biological in nature, I'd be more accustomed to something like "symptoms typically appear between five and six days after infection", which covers for outliers too but also sets the bound more definitely
    – roganjosh
    Commented Mar 4 at 18:10
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    @Lambie: "Within two or three weeks extends a range to any time from 1 day to 21 days." Note the nuanced difference between "within [two or three weeks]" (one reference point with an uncertain value = limit) and "Within [two] to [three] weeks" (two distinct reference points = range).
    – Flater
    Commented Mar 5 at 2:15
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    @Lambie: Your last comment makes me wonder if you are either not understanding what a range is, or actively disagreeing that "within" could be used to indicate a range. The dictionary explicitly has this usage covered, so I'm not sure what it is that you're commenting on here.
    – Flater
    Commented Mar 5 at 2:18
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(a) Symptoms will develop within five to six days after contracting the disease. This statement indicates a range of possible times for symptom onset. Symptoms could show up as early as five days after contracting the disease, or as late as six days.

(b) Symptoms will develop within six days after contracting the disease. This statement sets a maximum window for symptom onset. Symptoms must appear within six days, but could potentially show up earlier than five days.

Therefore, while both sentences might be interpreted similarly in casual conversation, they convey slightly different information regarding the precision of the timeframe.

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    Your answer says that that (a) "within five days" symptoms will develop either on day 5 or day 6, which suggests there will be no signs of symptoms on day 4 of contracting the disease. So why would a doctor, a website or whoever (it's time that users begin to tell us their sources) say "within" in the first place? Wouldn't they say "symptoms will manifest/appear/develop between five or six days". And how is this answer any different from @Astralbee's?
    – Mari-Lou A
    Commented Mar 4 at 17:30
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    @Mari-LouA Yes, I think the within versus on [days or day] is the point. But Astralbee says I'm wrong and cites the dictionary.
    – Lambie
    Commented Mar 4 at 17:53
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    @Mari-LouA "between five or six days" is not the same as "within five or six days". "Between" means that if you get symptoms, it will be on day 5 or day 6. "Within" means you could get symptoms anywhere from day 1 to day 6.
    – JeffC
    Commented Mar 5 at 18:21
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    @JeffC *Within" means you could get symptoms anywhere from day 1 to day 6. * but this answer doesn't say that it says Symptoms could show up as early as five days after contracting the disease, or as late as six days.
    – Mari-Lou A
    Commented Mar 5 at 18:37
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    @JeffC My use of "between" is correct if symptoms manifest either on day 5 or day 6. The use of "within" in example (a) is ambiguous. It could be any day before day 6 or it could refer to the very specific period between day 5 and day 6. In fact, Style's interpretation is different from yours. I am referring to sentence (a) not sentence (b) which I can go along with. I hope I've explained myself more clearly. TBC I didn't cast any downvote, I just queried the answerer's interpretation.
    – Mari-Lou A
    Commented Mar 5 at 18:55
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I think this is just a way of emphasizing the imprecision of estimates like this. I often find myself writing things like "around 5 or 6 years ago", which is clearly redundant: "around 5 years ago" already expresses that it might not be exactly that many years.

Biological processes are highly variable, so it's hard to be precise about how long something will take. "within 5 to 6 days" might mean that it's usually within 5 days, but occasionally 6 days. So if you don't experience symptoms within 5 days you're probably safe, but don't be too surprised if they appear the next day. But if you make it to 7 days, you're very likely to be safe.

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You can take a hypothetical example to test how you would receive the information. When Covid was a concern but between lockdowns, this was actually somewhat commonplace and real. Scenario:

  1. You go to a party
  2. Two days later you wake up feeling unwell
  3. A group chat goes around at lunch time of that same day to all attendees that Bob has just been diagnosed with Uhohitis. You look it up online and find:

A highly contagious, painful and chronic infection... Symptoms will develop within five to six days after contracting the infection.

  1. Evaluate now whether you feel like there is any kind of definite lower bound set by the inclusion of that "five days" for you to take some kind of comfort from. Does it provide any assurance to you that your sudden-onset-sniffles isn't going to develop into Uhohitis because it's only been two days?

The other answers suggest that it sets some kind of lower bound, however implied it may be. I'd argue that it adds absolutely none - the point of medical information/language is to be as clear and as precise as possible with something that is inherently non-deterministic (in biology there will always be outliers). My answer is therefore that they are the same - it's no different to "within six days".

Without symptoms I'd take "Symptoms will develop within five to six days after contracting the disease" on day five as being "I'm in with a shot here to dodge this one" and after day six being "Ok, I made it". If I had any kind of symptom at all, no matter the period after exposure, I'd be really concerned. Add to that, "will develop" suggests that asymptomatic infection is not possible - you will have symptoms if you're infected.

I'd argue that "symptoms typically appear between five and six days after infection" is a far-better representation of the information if indeed they wanted to set a lower bound and suggest that two days just isn't practical in linking my party attendance and my feeling unwell. There will always be outliers, but I think the general public understands this about incubation periods even if only instinctively, and it is much better at setting expectations.

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    The problem is whether within 5 to 6 days has a lower bound day that is day 1. I say it does and it extends UP TO at most day 6. Do you agree?
    – Lambie
    Commented Mar 5 at 18:03
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    @Lambie that's precisely my point that I made - "The other answers suggest that it sets some kind of lower bound, however implied it may be. I'd argue that it adds absolutely none". I used the example as a way of sense-checking whatever implied lower bound there was. If you're not sick, you might take is as some trivial milestone to make it to day 5. If you are sick, that lower bound goes out the window and you would panic from day one.
    – roganjosh
    Commented Mar 5 at 18:08
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    It sets no lower bound. I think we aren't using the word bound the same way: For me, the range is Day 1 through to Day 6. So, the lower bound is Day 1 and the upper one is Day 6. I read through your answer and did not understand what I just explained. Also, it's easier to follow if you say sentence one and two, or whatever.
    – Lambie
    Commented Mar 5 at 18:10
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    Given that time can only move in one direction, the absence of a specified lower bound means that the clock starts ticking at the moment of exposure. It obviously cannot be the day/week/year before the exposure so I didn't feel the need to say that. The lower bound is determined by the physics of the universe unless specified otherwise
    – roganjosh
    Commented Mar 5 at 18:15
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    But that is exactly the issue. Read Astralbee's answer who says it is two different things and that's precisely because of how one interprets the bounds of this time periods that say: within 6 days or within 5 or 6 days.
    – Lambie
    Commented Mar 5 at 18:17
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Anecdotally, I have seen (and been confused by) a policy that said that something was requested "within 3-6 months". I initially took it as a suggestion to wait at least 3 months, but asked for clarification, and was told that 3 months was not a minimum.

It is confusing because logically, "within 6 months" would have conveyed the rule more precisely. My interpretation is that people may be "imprecise" because they are simultaneously indicating a maximum and an expected typical amount of time. (That is, normally 3-6 months is expected, and 6 is the maximum, but 3 is not a minimum.) So, "within 3-6 months" in this case probably meant "within typically at least 3 and definitely no more than 6 months".

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    Your final sentence as it stands is contradicting the rest of your answer; I think you mean suggest that "within 3-6 months" is probably trying to convey "definitely within 6 months, and typically between 3 and 6 months".
    – ryang
    Commented Mar 12 at 1:34
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Symptoms will develop within five to six days after contracting the disease.

Adding to Martha's, Bamar's and roganjosh's answers: let's charitably interpret the speaker's phrasing, that is, assume that they aren't being sloppy:

  1. Perhaps because they simply can't recall, or maybe due to the literature being conflicting, they are unsure where exactly between the 5th and 6th days the symptoms' onset's upper bound is.

    If they had meant that the upper bound is variable between the 5th and 6th days, they would have simply said “within six days”.

  2. “Within five to six days” technically must have the same lower bound as “within six days”: symptoms could develop as early as immediately.

In all likelihood though, the speaker is being sloppy, in which case I think nschneid's answer is on to something: the speaker is probably trying to say that symptoms will develop within six days—typically between the 5th and 6th days.

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    Thank you all very much. I was asked if the example sentences were invented by me. They were, but I think one sees this kind of thing a lot. All you have to do is search 'within five to six days' on googlebooks, You'll find loads of examples. And there's nothing special about 'five and six days'. I think this is a real problem. Nobody seems to find the problematic sentence 'unnatural', although it seems illogical to some people (including me), I think to be on safe side, I'd assume that it is ambiguous.
    – azz
    Commented Mar 10 at 23:13
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    @azz I just did a google search and phrases like "within five to six days" are indeed common. Anyhow, my answer is trying to charitably explain that the speaker is thinking, "I can't recall whether symptoms are known to develop within 5 days or within 6 days or even within 5.5 days; whatever the case, it is definitely accurate to say that symptoms develop within 5 to 6 days."
    – ryang
    Commented Mar 12 at 1:29

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