When historians are writing, they use BC and AD with the date, e.g.:

Robinson discovered the island in 202 BC.

If historians are uncertain about the date, is there a simple and short notation they can add to the date, to indicate the uncertainty? I'm looking for something like this, but more professional:

Robinson discovered the island in 202 BC (?).

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    All three answers assume that the question is about approximate dates (that, in the example, we are not quite certain that it happened precisely in 202—maybe it was 201 or 203). However, historians, particularly when they investigate distant eras, may sometimes deal with uncertainties of a very different kind. It could be that, according to one hypothesis, 'Robinson' discovered the island in 202 BC, but that according to a different hypothesis, he lived many generations later, and discovered it in 49 BC. Is the question only about the uncertainties of the former kind? – jsw29 Sep 3 at 14:34
  • I'll try to give an example. Lets say Robinson was stranded, he didn't do a good job of tracking the dates. He was rescued after what he guesses was 10 years, so we work backwards to do the math, but historians aren't sure. – Village Sep 3 at 17:07
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    Does this answer your question? What word can I say if I want to give approximate number? – Decapitated Soul Sep 4 at 11:56
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    Nowadays CE has replaced AD and BCE has replaced BC, for political correctness. – Phil Freedenberg Sep 4 at 13:56


(written abbreviation c); (ca)
(used especially with years) approximately:
He was born circa 1600.

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    You should refer to this, for example. Nothing is confusing about the resulting post, though some lines (the last ones) are nicer to look at. – Nij Sep 5 at 1:28

I don't know whether historians use it in this way, but one of the many uses of the tilde (~) is "approximation".

Robinson discovered the island in ~202 BC.

would therefore be read/understood as

Robinson discovered the island in approximately 202 BC.

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    Well, yes, except that the round figure would be ~200 BC. You don't report data with three-figure accuracy when you're simultaneously reporting uncertainty about the data. – John Lawler Sep 3 at 13:53
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    @JohnLawler I think that depends on just how uncertain you are, but in this particular context "~200 BC" is probably more appropriate, as you say. – Anthony Grist Sep 3 at 14:06
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    @JohnLawler Except this isn't math. If you pulled from a sketchy historical sources mentioning 202BC, it would be misleading to say ~200BC. For example, if I told you that about 7 years ago something happened to me, and you retell the story to someone else, you aren't going to round up and say that it happened 10 years ago because for all you know, I know for a fact it did not happen earlier than 5 years ago but later than 10 years ago – DKNguyen Sep 4 at 1:04
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    @JohnLawler The tilde implies some unspecified error margin around the year. Significant figures don't apply to years because the AD/BC boundary is an arbitrary point on the timeline. Let me define 0 AA (Anno Arbitrium) as 329 BC; now your "round" 200 BC is an "ugly" 129 AA. Simply counting significant figures is a very poor way of dealing with uncertainty anyway. Don't even get me started on "round" being biased (again: arbitrarily) to base 10. – Carl Leth Sep 4 at 7:12
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    @JohnLawler Significant figures are numbers that convey meaningful accuracy. If something is given as 202 with three significant figures, that means that 202 is significantly more likely that the other possibilities, but it could be 201 or 203. – Acccumulation Sep 5 at 3:49

The Oxford English Dictionary prepends the letter c to indicate an approximate year:

c1400 (▶?c1380) Pearl

a quotation from a manuscript of around (= circa) 1400 preserving a text probably composed around 1380. (The symbol ▶ preceding a date indicates that this is a date of composition, not a manuscript date.)

This is also used in the Middle English Dictionary, for example.

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If historians are uncertain about the date, is there a simple and short notation they can add to the date, to indicate the uncertainty? I'm looking for something like this, but more professional:

Robinson discovered the island in 202 BC (?).

Yes, there is a symbol and it is (Ahem......) (?).
Your use of (?) is professional and correct.

According to Sussex University Website:

The question mark also has one minor use: it may be inserted into the middle of something, inside parentheses, to show that something is uncertain.
The question marks on the poet's birth and death dates indicate that those dates are not certain.

Summary of Question Marks:

  • Use a question mark at the end of a direct question.
  • Do not use a question mark at the end of an indirect question.
  • Use an internal question mark to show that something is uncertain.

[University of Sussex]

Also from White Smoke:

Use a question mark enclosed in parenthesis (?) if a date or another number is unknown or doubtful among the experts. Do not use a question mark to communicate that you are unsure of the information you write, as this weakens the authority of your writing.
Joan of Arc, 1412 (?) – 1431, is considered a French heroine.

Also see Jozef Pelsudski Institute.

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    Note that ? is totally different in meaning from circa. – Fattie Sep 4 at 16:38
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    @Fattie, Yes, that's why I've quoted OP's question ("... symbol for uncertainty"). Circa is used for approximation. (It's (?), not ?, though.) – Decapitated Soul Sep 4 at 16:40

The tilda ' ~ ' is used to express an approximation:

Robinson discovered the island in ~202 BC. = Robinson discovered the island in approximately/about/ in some year close to 202 BC. (See https://en.wikipedia.org/wiki/Tilde)

The question mark is used to give a date which is, in the view of the writer, probably correct but over which there is some doubt.

Robinson discovered the island in 202 BC(?) = It is thought that the year was 202BC when Robinson discovered the island.

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  • Yes; an important distinction. They show different types of uncertainty. << Robinson discovered the island in ~202 BC(?) >> uses both caveats. – Edwin Ashworth Sep 5 at 13:44
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    As there seems to be a proliferation of answers on this page, it might help the future visitors to it, if it is made explicit how this answer is related to the ones already posted: it combines the answers given by Anthony Grist and by Decapitated Soul, and offers an account of when each of them is applicable. – jsw29 Sep 6 at 16:09

Re the currently low-voted answers: I would caution that if you're going to use "(?)" to indicate uncertainty in formal written English, (A) don't, and (B) be very careful about its placement.

Robinson discovered the island in 202 BC(?).

Does the writer mean that Robinson definitely discovered the island, maybe in 202 BC? Or that it's uncertain whether Robinson was the discoverer at all? Or that the writer is certain that Robinson discovered the island in 202, but isn't sure if it was BC or AD?

Robinson discovered the island in 202(?) BC.

This version reads much clearer to me personally. The "(?)" is clearly attached to the date "202"; Robinson's discovery is not in question, and neither is the fact that the "202(?)" refers to a time BC. Compare to alternatives such as

Robinson(?) discovered the island in 202 BC.

Robinson discovered the island(?) in 202 BC.

However, if you mean something, it's almost always clearer to just say that thing in English, rather than trying to encode it in the placement of punctuation.

Robinson is thought to have discovered the island in 202 BC.

The island was discovered by Robinson; Friday gives the year of its discovery as 202 BC, but other historians have contested that timeline.

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  • Yes, you are quite right that, generally, the best thing to do is to spell out what the uncertainty is. Sometimes, however, spelling that out would distract the reader from the point that the author is trying to make; it is in such cases that a scholar needs to resort to the question mark, which makes it possible to conscientiously acknowledge the uncertainty without dwelling on it. – jsw29 Sep 6 at 17:00
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    @jsw29: My point is that there's a difference between "to conscientiously acknowledge the uncertainty" (excellent) and "to conscientiously acknowledge an uncertainty" (usually bad, if the reader has no clue which of the writer's many factoids are supposed to be uncertain). – Quuxplusone Sep 6 at 19:25

According to New Hart's rules: the handbook of style for writers and editors, Oxford University Press, 2005, p. 183, ISBN 978-0-19-861041-0, the multiplication sign (×) may be used when the exact date is unknown, but some bounds are established:

When referring to events known to have occurred between two dates, historians often employ a multiplication symbol 1225 × 1232 (or in some styles 1225 × 32) means 'no earlier than 1225 and no later than 1232'. The multiplication sign is also useful if one element of a range is itself a range: 1225 × 32 - 1278

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    Nice! But I'm sure that if I ever encountered this notation in real life, I would have no idea what the writer meant and no way to google for the answer. – Quuxplusone Sep 6 at 20:04

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