Iudex reum interrogat, sed reus nihil respondet.

Because the same word is doing two different jobs.

• reum is accusative singular, used for the direct object: the judge questions the defendant.
• reus is nominative singular, used for the subject: the defendant answers nothing.

So Latin changes the ending to show the noun’s role in the sentence.

We know from case.

• iudex is nominative singular, the case normally used for the subject.
• reum is accusative singular, the case normally used for the direct object.

So iudex reum interrogat means that the judge is doing the questioning, and the defendant is being questioned.

In English, word order does most of that work. In Latin, endings do much more of it.

iudex is nominative singular and belongs to the third declension.

Its dictionary form is:

• iudex, iudicis = judge

That genitive iudicis shows the stem iudic-, which is why other forms look different, such as:

• nominative: iudex
• accusative: iudicem
• genitive: iudicis

A learner may expect a subject noun to end in -us, but many Latin nouns do not. iudex is a third-declension noun, so its nominative singular has its own pattern.

interrogat is:

• present tense
• third person singular
• active voice
• indicative mood

It comes from interrogare, meaning to question or to ask.

So interrogat means he/she/it questions or is questioning. Here the subject is iudex, so it means the judge questions.

respondet is also:

• present tense
• third person singular
• active voice
• indicative mood

It comes from respondere, meaning to answer or to reply.

So respondet means he/she/it answers or replies. Here the subject is reus, so it means the defendant answers.

In the present indicative active, -t is the normal ending for third person singular.

So:

• interrogat = he/she/it questions
• respondet = he/she/it answers

That ending tells you the subject is a single person or thing, not I, you, or they.

nihil means nothing.

In this sentence, it goes with respondet and means that the defendant gives no answer or says nothing in reply.

So nihil respondet is stronger and more concrete than just saying does not answer. It suggests he answers nothing or he says nothing.

Because Latin often leaves out words that are easy to understand from context.

Here, once we have already been told that the judge is questioning the defendant, it is natural to understand that the defendant is not replying to the judge.

Latin could express the person replied to in other ways if needed, but it does not have to. The sentence is perfectly complete as it stands.

Here it is functioning as a noun, yes.

Originally, reus is an adjective meaning something like accused or involved in a legal case, but Latin often uses adjectives substantively, meaning as nouns.

So reus can mean:

• the accused man
• the defendant

That is why you can see forms like:

• reus = the defendant, as subject
• reum = the defendant, as object

Because Latin has no definite or indefinite article.

So Latin does not have separate words for:

• the
• a
• an

That means iudex can mean the judge or a judge, and reus can mean the defendant or a defendant. Context tells you which is most natural.

It is important for style and emphasis, but less important for basic grammar than in English.

Because the endings already show the grammatical roles, Latin could rearrange the words without changing the core meaning very much. For example, the sentence could be reordered and still mean the same thing.

The given order is natural and clear:

• Iudex reum interrogat = first clause
• sed reus nihil respondet = contrasting second clause

The conjunction sed marks the contrast: the judge asks, but the defendant gives no answer.

In classical Latin spelling, the letter J was not used the way it is in English. You will often see the word written as iudex.

Likewise:

• iulius instead of Julius
• iam instead of jam

In many older books or traditional editions, you may still see judex, but iudex is the standard classical-style spelling.

In a classical pronunciation, roughly:

• iudex ≈ YOO-deks
• reum ≈ RAY-oom or REH-oom depending on how carefully you pronounce the vowels
• interrogat ≈ in-ter-roh-gaht
• sed ≈ sed
• reus ≈ RAY-oos
• nihil ≈ NEE-hil or sometimes NIH-il
• respondet ≈ re-SPON-det

A few useful points:

• i at the start of iudex sounds like English y
• v in classical Latin is pronounced like w, though this sentence does not contain one
• final -t is pronounced clearly

So the beginning iudex is not like English judge at all.