Hi, I know this is a bit of a strange set of questions as it is not actually related to a specific bit of history. Full disclosure, I am a PhD student looking into how uncertainty in historical data can be better represented in visualisations (particularly timelines). One thing that I am trying to do is understand a bit more about the terms that come up when dates are described.
When applied to dates what does circa mean to historians?
How does it compare to other terms (e.g. approximately, about)?
Are there any academic guidelines or documentation on when or how to use or interpret it? Or is it like an unwritten rule?
What do you think affects how the overall range of a date with circa is perceived?
It just means "approximately." Like, we don't know for sure that Hans Folz was born in 1435, but based on the other dates in his life (arrival in Nuremberg, attainment of meister status in various professions, death, etc), we can guess he was probably born around then.
So you'd say Hans Folz (c.1435-1513)
Sometimes an alternative is to use a slash to indicate a range--in this case, Caroline Huey uses "1435/40-1513." This can be conceptually helpful in that it preserves the fuzziness a little better, avoiding the whole 'names-dates-FACTS' mentality of a high school history class to some extent. Since the slash is also used in late medieval-early modern scholarship when the calendar changed from the new year landing in March to January, though, the slash to indicate ambiguity can be confusing. Most people use c. or circa.
Are there any academic guidelines or documentation on when or how to use or interpret it? Or is it like an unwritten rule? What do you think affects how the overall range of a date with circa is perceived?
No, there are no guidelines or even unwritten rules for interpreting what sort of a range is meant by "circa". In some ways, this is good! If it specifically meant "this year as well as two on either side", it would be too confining in some cases and imply too much in others. I try to use it only for "I can't say exactly, but around this year," but I have certainly seen it used to mean, at different times, "I'm almost absolutely positive it was in this year," "the 1870s but I'm saying c. 1870 because I don't understand how this works," and "basically the middle of the century."
When I'm writing about prehistory here I reflexively add "circa", "approximately" or "about" to dates (they're all the same in my mind) because in prehistory all dates come with substantial uncertainty. In a more technical setting, you'd be expected to attach a quantitative estimate of that uncertainty: at the very least a confidence margin (e.g. "34920–31250 BP at a 95% confidence level"); but ideally the full probability distribution, which is usually visualised with a histogram.
Reading through this thread it is interesting the range of uncertainties that circa can imply. I usually round things to the nearest millennium, so "pottery was invented c. 6000 BCE" means 6500–5500 BCE.
