Autrefois, on croyait que la terre était plate.
Jadis, on croyait que la terre était plate.
Dans le temps, on croyait que la terre était plate.
How do these synonyms actually differ in nuances and usages?
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Sign up to join this communityI would say that they all defined a period of time fully contained in the past.
"Jadis" will be used more often in literature or sustained language and it will be used more often for historical or events far into the past. You can also use "naguère" as a synonym.
"Dans le temps" implies a bigger break between past and present time than "autrefois". And I think it is more often used orally than "jadis" or "naguère".
"Autrefois" come from "autre" and "fois" which means "other times".
"Jadis" come from old french "ja a dis" which means word by word "already", "is", "days" (wiktionary).
(XIIe siècle) Contraction de l’ancien français « ja a dis », proprement « il y a maintenant des jours », composé de ja (« maintenant, déjà, ... »), de a du verbe avoir à la 3e personne (ici signifiant "il y a") et de dis (di au singulier) signifiant « des jours » (le même di que dans lundi, mardi, mercredi, etc.)
As synonymous words you can use "anciennement", "d'antan", "temps passé", "naguère"...
Autrefois (TLFi) : À une époque appartenant à un passé révolu, généralement opposée à l'époque actuelle et pouvant être précisée par le contexte.
Jadis (TLFi) : Adv. Dans un passé plus ou moins lointain; il y a longtemps. Synon. plus cour. autrefois.
Dans le temps (TLFi) : (dans les temps, vieilli); Autrefois, dans le passé.
It can be seen from the définitions that all three expressions have the same meaning; they can be used for periods of time not too far back into the past; how far is a difficult question to answer;
One will rather say this;
As relates to use in intermediate position in a sentence, it can be seen from un ngram that as the frequnecy of use of "dans le temps" has increased to be finally more important than that of "autrefois" and "jadis", that of the latter two has decreased as they have been replaced by the former.
As relates to use at the beginning of a sentence, surprisingly, "autrefois" and "jadis" are found more often (ngram).