Qui, quae, quod vs. quis, quid Due to similarities in forms and some overlappings in the uses of their English equivalents, some people have trouble distinguishing between those Latin words and knowing when to use which. I'll try to make things clear in the following. It is aimed principally at those who are already a bit familiar with those words, but may not always be sure of the exact differences between them. A. Qui, quae, quod A.1. Here is a list of the most basic uses of qui, quae, quod: Qui, quae, quod can be: 1) A relative pronoun, "who", "which", "that", representing someone or something mentioned (often previously mentioned, but it can sometimes be after) or implied in the main clause. This someone or something is called "antecedent". In the following examples, I have underlined the relative pronouns, and bolded the antecedents when there was one expressed. a. Illa femina quam heri vidisti uxor Quinti est = "That woman whom you saw yesterday is Quintus's wife." b. Qui me iuverunt, eos iuvabo, nec ullos alios = literally "Who have helped me, those I will help, nor any others" = "I will help those who have helped me and no others." (This construction and word order puts a rather strong emphasis on "those".) c. Qui te rident stulti sunt = "[Those] who laugh at you are stupid." (The antecedent is here left implied in the Latin.) d. Calamus quo scribis meus est = "The pen that you're writing with (with which you're writing) is mine." e. Claudiam, quae in lecto iacebat, surgere iussi = "I ordered Claudia, who was lying on the bed, to get up." N.B. In English, relative pronouns can sometimes be left out. E.g. you can say "the woman you saw yesterday" instead of "the woman whom you saw yesterday" or "the pen you're writing with" instead of "the pen that you're writing with" or "the pen with which you're writing". This does not happen in Latin; in Latin, relatives are always expressed. 2) An interrogative adjective, used together with a noun in a question, whether direct or indirect, concerning that noun: "which [insert noun]?", "what [insert noun]?" Examples: a. De quo libro loqueris? = "What/which book are you talking about?" (direct question) b. Quae picturae tibi maxime placent? = literally "Which paintings are most pleasing to you?" = "Which paintings do you like most?" (direct question) c. Interrogavit cui puero dedissem pecuniam = "He asked which boy I had given the money to." (indirect question) d. Scio qui poeta hos versus scripserit = "I know which poet wrote these verses." (indirect question) N.B. When "which" means which of two, the more specific uter, utra, utrum is generally preferred to qui, quae, quod. 3) An interrogative pronoun, representing in a question, whether direct or indirect, a noun previously mentioned or implied: "which?", "which one(s)?" out of a more or less definite group mentioned or implied. Examples: a. Ecce quattuor pira. Quod vis? = "Here are four pears. Which one do you want?" (direct question) b. Qui ex his servis dignissimus manumissione est? = "Which one of these slaves is most worthy of manumission?" (direct question) c. Ex omnibus istis quos legisti libris, qui maxime placuit? = "Out of all those books you've read, which did you like most (literally, "which was most pleasing")?" (direct question) d. Quem horum ciborum tibi malis edendum dari? = "Which of these foods would you prefer to be given to eat?" (direct question) e. Vidi quidem equos, sed non currentes, ergo nescio qui velocissimus sit = "I did indeed see the horses, but not running, so I don't know which one is fastest." (indirect question) When it is about people, "who" is sometimes an acceptable translation too. N.B. The N.B. to 3) applies here too. 4) Qui and quae can sometimes mean "who" even when that "who" isn't out of a definite group, but this will be explained later after the basic interrogative "who", quis, has been introduced. A.2. A couple more uses of qui, quae, quod. If you feel that the preceding is already enough for you to take in at once concerning qui, quae, quod, you may skip this part for the time being. 1) When qui, quae, quod is used as a relative, it sometimes happens that the antecedent is attracted into the relative clause. In that case, qui, quae, quod appears to be technically used as a relative adjective. Example: Quo die nuntiata est mors regis, magnus luctus erat in urbe = literally "On which day the king's death was announced, there was great mourning in the city" = "The day (on which) the king's death was announced, there was great mourning in the city." 2) Qui, quae, quod can be used in places, like the beginning of a sentence, where in English one would more naturally use a personal pronoun (he/she/it/they) or a demonstrative (that/this), or even just a definite article (the). In those cases, it is roughly equivalent to (et) is/ea/id, but qui, quae, quod produces sort of a more fluid transition, as if still linking the new sentence to what preceded. It may be used this way both as a pronoun and as an adjective. Example with it as a pronoun: Nuntius advenit ac petivit ut adduceretur ad regem, missum enim se a fratre eius esse gravem quandam rem nuntiaturum. Duxerunt eum per castra. Qui cum in tabernaculum regis intromissus esset, rex pallescere visus est... = "A messenger arrived and asked to be led to the king, for [he said] he had been sent by the latter's brother to announce some serious matter. They led him through the camp. Who when had been let into the king's tent (i.e. in normal English, "When he had been let into the king's tent"), the king seemed to grow pale..." Example with it as an adjective: take the above, and just change qui cum in tabernaculum regis intromissus esset to qui nuntius cum in tabernaculum regis intromissus esset, literally "which messenger when had been let into the king's tent...", i.e. "when that messenger had been let into the king's tent..." B. Quis, quid Quis, quid is an interrogative pronoun, used in questions, whether direct or indirect; basically, quis means "who?", "what person?", and quid means "what?", "what thing?", in the broadest, most indeterminate sense possible. Examples: a. Quis hoc fecit? = "Who did this?" (direct question) b. Quid arbitraris? = "What do you think?" (direct question) c. Nescio quid cras acturus sim = "I don't know what I'll do tomorrow." (indirect question) d. Dicam tibi quis mihi hodie praestaturus sit cenam: tu = "I will tell you who will offer me dinner today: you." (indirect question) e. Quis nostrum hoc ignorat? = "Who of us is unaware of this?" (direct question) Note that when, in English, "what" is used adjectivally (i.e. together with a noun, as in "What animal is that?"), one does not use quid in Latin, but the appropriate form of qui, quae, quod according to the gender etc. of the noun (see A.1.2)). Quis, beside its uses as a pronoun, may also be used adjectivally with a masculine noun, much like qui, as an interrogative adjective (see A.1.2)), would be. E.g. Quis finis erit huius belli? = "What end will there be to (lit. "of") this war?" The same thing does not happen with quid and neuter nouns; it only happens with quis and masculine nouns. C. Quis vs. qui (and the latter's feminine quae) in the sense of interrogative "who?" (what I alluded to in A.1.4)) In theory, quis is asking for someone's identity: just for who the person is — tell me "it's him!" — or basic information like their name, origin, and such; whereas qui is asking more for someone's character, like what sort of person they are. E.g. Scin quis ego sim? = "Do you know who I am?" ---> implying, maybe, something like "Do you know that I'm X, born of parents F and M, living in town T, doing job J?"; Scin qui ego sim? = "Do you know who (which/what (sort of) man) I am?" ---> implying "Do you know my character, what sort of person I am?" This dictinction, however, may not always be stricly adhered to. And it is less adhered to when the person one is asking a question about is known to be a woman, because then quae may be used as if it were simply the feminine of quis (which has no distinctively feminine form, and Romans apparently felt a certain need for one, which led them to use quae), without necessarily implying that one is asking for the woman's character rather than her mere identity; this even though quis was initially common gender and may be used for a woman as well. Thus, "Who's that woman?" may translate to either Quae est illa mulier? or Quis est illa mulier? The feminine use of quis, however, appears to have been more common in early Latin than in classical. I hope this post has helped. One last word: the concepts of relative clauses and indirect questions having been mentioned in this post, and the difference between them being often crucial in determining whether one should use the relative pronoun qui, quae, quod or the interrogative pronoun quis, quid, if you are not clear on the difference, you may have a look at this other post of mine.