Tonsor barbam novacula radit.

Because barbam is the direct object of radit (shaves). In Latin, a direct object usually goes in the accusative case.

• barba = beard (dictionary form, nominative singular)
• barbam = beard as the thing being shaved (accusative singular)

So tonsor barbam radit means the barber shaves the beard.

Because novacula is not the direct object. It tells you the means or instrument used to do the action: with a razor.

Latin often uses the ablative case for this, called the ablative of means or ablative of instrument.

So:

• barbam = what is shaved
• novacula = what it is shaved with

That is why novacula is ablative singular here.

On its own, novacula could look like either nominative singular or ablative singular, because first-declension nouns have the same ending in those forms.

You figure it out from the sentence structure:

• tonsor is clearly the subject
• radit is the verb
• barbam is the direct object
• that leaves novacula to function as an ablative of instrument: with a razor

So grammar and meaning together show that novacula is ablative here.

Latin has no articles like English the or a/an.

So tonsor can mean:

• the barber
• a barber

Likewise:

• barbam = the beard or a beard
• novacula = with a razor or with the razor

You decide from context which English wording is best.

Tonsor is a noun, and here it is the subject of the sentence.

It is in the nominative singular, meaning barber.

So the basic structure is:

• tonsor = subject
• radit = verb
• barbam = direct object
• novacula = instrument

Radit is a verb in the:

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

So it means he/she/it shaves.

Because the subject is tonsor, we understand it as the barber shaves.

The dictionary form is rado, radere, rasi, rasum, meaning to scrape, to shave, or to shave off.

In this sentence, radit comes from that verb and means shaves.

A learner should notice that this is a 3rd-conjugation verb:

• rado = I shave
• radit = he/she/it shaves

Yes, Latin word order is much freer than English word order because the endings show each word’s role.

This sentence could be rearranged in several ways without changing the basic meaning, for example:

• Tonsor barbam novacula radit
• Tonsor novacula barbam radit
• Barbam tonsor novacula radit
• Novacula tonsor barbam radit

The different orders may change emphasis slightly, but the forms still show:

• tonsor = subject
• barbam = object
• novacula = instrument
• radit = verb

Latin often places the verb near the end, as in this sentence.

Yes. Latin often leaves out the subject pronoun, and sometimes even the subject noun if it is already clear from context.

For example:

• Barbam novacula radit = He/she shaves the beard with a razor

The verb radit already tells you the subject is third person singular. But if you want to state explicitly that it is the barber, you include tonsor.

Because rado specifically means to scrape/shave, and it fits well with shaving a beard using a razor.

A learner may know another verb such as tondeo, which often means clip, shear, or trim. That verb is commonly used for cutting hair, wool, and similar things.

So radit is a good choice here because the action is specifically shaving.

Yes. Novacula is a noun meaning razor.

Its basic forms are:

• novacula = nominative singular
• novaculae = genitive singular

It is a first-declension noun, even though it refers to a tool rather than a person.

In this sentence, it is in the ablative singular: novacula = with a razor.

Yes. It shows a very common pattern:

subject + accusative object + ablative of instrument + verb

Here that gives:

• tonsor = subject
• barbam = accusative object
• novacula = ablative of instrument
• radit = verb

This is a useful model for many other Latin sentences. Once you recognize the cases, the sentence becomes much easier to read.