Keller's Learn to Read Latin says:

The adjective Idem, eadem, idem is formed by the addition of the suffix -dem to the demonstrative adjective is, ea, id.

What does suffix -dem mean? I couldn't find it in the Oxford Latin Dictionary.

  • 1
    @Joonas why did you tag my post with pronouns? They are adjectives, mentioned in the quote.
    – Tim
    Apr 3, 2023 at 13:33
  • 2
    I would say that both idem and is are pronouns. The boundary between the two concepts isn't always clear, and there are different conventions. Feel free to add a tag for adjectives if you think that is a more apt name, but do keep the pronoun tag as many will see those words as pronouns.
    – Joonas Ilmavirta
    Apr 3, 2023 at 14:05

1 Answer 1


In practice it means nothing. What I mean by this is that the suffix -dem has only very special uses, you cannot use it productively on new words, and it does not have an easily predictable effect on the meaning. It is therefore practical not to treat -dem as a suffix, apart from remembering how to inflect the pronoun idem. It therefore makes perfect sense for the suffix not to appear in dictionaries.

The etymology of the suffix -dem and whether it is a misinterpretation of an actual suffix -em as mentioned by Wiktionary I will leave to others. That is interesting, but not very relevant for learning to use Latin.

  • Thanks. I can't visit Wiktionary, due to the Great Firewall. Could you copy and paste here from Wiktionary? I can't see screenshot hosted on imgur either, because imgur is blocked.
    – Tim
    Apr 3, 2023 at 13:32
  • @Tim Wiktionary says: "Misinterpretation of -em. When the old ablative cases of is, eōd, eād, became eō, eā, the true forms eōd-em, eād-em were interpreted as eō-dem, eā-dem. The neuter nominative singular id-em is natural and gives earlier emem (= later eundem). The new marker -dem then served to create totidem, tantumdem, ibīdem, etc. Compare tam-en with its later doublet: tan-dem (← *tam-dem)." But as I said, whether that is a good description should be explained someone more etymologically qualified than me.
    – Joonas Ilmavirta
    Apr 3, 2023 at 14:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.