The other day, I was talking to a friend about how we teach history in school (IE grades 1-12.) I thought about the fact that "conventionally," people living centuries to millennia apart are grouped into the same era, despite living in societies that would be fundamentally alien to one another, not to mention potentially closer to a "different" era.
I know that there are some "periods" that cover the end of one of the "conventional" periods and the start of another (e.g. Late Antiquity,) but do academic historians still use general categories like Ancient, Medieval and Modern? Are these seen as dated or presentist? If they are used, what practical purpose do they serve, and what meaningfully separates one period from its successor?
Apart from the history of the inception of the concept, historians themselves never really separated history completely into three separate eras -- but they did separate the historiography and research fields, and that is easy to confuse. The latter occurred primarily because in its infancy, academic history was largely eurocentric (and I am tempted to say eurocentric, period!): Modern academic history really began in the 18th century and looked back at the Roman and Greek period as "the classical beginnings", hence lumped everything into that era as "ancient", and the medieval concept of "medievality" determined the second era, while the renaissance, the age of discovery and/or the advent of protestantism by and large was considered the end of the medieval world (hence "modern" history from thereon out). It is noteworthy that there is an increasing distinction (since the early 20th century) between "early modern" and "late modern", and more recently, "contemporary" history. So the old three-split has long given way to more cracks into future sub-fields.
The reason for the first three-ways split as academic subfields do still make sense: History is about the reading of historical sources in their context, and for that sub-specialization always made sense in terms of efficiency: knowing medieval Latin is of little use to a historian of early Rome, and ancient Greek is almost useless to a scholar of 14th century French heraldry; medieval coats of arms or Merovingian heritage rights are of little gain to a historian of the late British Empire, a 20th century diplomatic historian is better off knowing some French than the agricultural reform attempts of the Gracchi, etc.
In short: the division of the fields into three (or more) sub categories make sense because of simple and obvious limitations to our time as humans on this Earth. They do not exist to artificially separate historical epochs or research fields from each other (though it might sometimes seem that way, looking at school books). Some of the greatest historians could traverse these subfields with ease, and no one gave them trouble for it.