Mater cultrum sub mensa relinquit, ne infans eum capiat.

Because mater is in the nominative case, which is the case normally used for the subject of a Latin sentence.

• mater = mother
• It is the person doing the action of relinquit.

So mater relinquit means the mother leaves.

Cultrum is in the accusative singular, because it is the direct object of relinquit.

The verb relinquit means leaves or leaves behind, and the thing being left is the knife:

• culter = knife
• cultrum = knife as a direct object

So:

• mater cultrum relinquit = the mother leaves the knife

Because sub can take either the ablative or the accusative, depending on the meaning.

• sub + ablative = under in the sense of location
• sub + accusative = to a place under in the sense of movement toward

Here the knife is already being left under the table, so this is location, not motion.

That is why Latin uses:

• sub mensa = under the table

If it meant something like she puts it under the table, you might expect sub mensam.

Mensa is ablative singular.

It is ablative because it follows sub in a meaning of place where or location:

• sub mensa = under the table

So the ablative here tells you where the knife is being left.

Here ne means so that ... not or lest.

It introduces a negative purpose clause. In other words, it explains the mother’s purpose:

• Mater cultrum sub mensa relinquit = the mother leaves the knife under the table
• ne infans eum capiat = so that the child may not get it / lest the child get it

So ne does not simply mean ordinary not. It specifically introduces a clause of intended prevention.

Because after ne in a purpose clause, Latin uses the subjunctive.

So:

• capit = gets / takes in the indicative
• capiat = may get / might get in the subjunctive

In this sentence, the mother leaves the knife under the table in order that the child not get it, so Latin uses:

• ne infans eum capiat

This is a very common construction:

• ut + subjunctive = positive purpose
• ne + subjunctive = negative purpose

Because the main verb is relinquit, which is present tense. That puts the sentence in primary sequence, and Latin normally uses the present subjunctive in a purpose clause after a present main verb.

So:

• main verb: relinquit = present
• subordinate verb: capiat = present subjunctive

If the main verb were past, you would usually expect the imperfect subjunctive instead.

Eum refers to cultrum.

It means him/it in the accusative singular masculine, and here it means it.

Why masculine? Because culter is a masculine noun, so the pronoun referring back to it must also be masculine:

• culter = masculine
• cultrum = accusative singular masculine
• eum = accusative singular masculine pronoun = it

So ne infans eum capiat means so that the child may not get it, where it = the knife.

Latin can do either, but using a pronoun is very natural once the thing has already been mentioned.

So after cultrum has been introduced, eum is enough to mean it. This avoids unnecessary repetition, just as English often does.

• first mention: cultrum
• later reference: eum

Infans can refer to either a male child or a female child. It is often treated as a noun of common gender.

So in this sentence, infans simply means the child / the baby, without necessarily telling you whether the child is a boy or a girl.

The grammar of eum does not refer to infans here; it refers to cultrum.

Latin word order is much more flexible than English word order because Latin uses case endings to show grammatical function.

In this sentence:

• Mater = subject
• cultrum = direct object
• sub mensa = prepositional phrase
• relinquit = verb
• ne infans eum capiat = purpose clause

English depends heavily on position, but Latin does not need to. So Latin can place words in an order that highlights meaning, emphasis, or style.

This sentence is actually quite natural:

• subject first
• object before the verb
• purpose clause at the end

It can mean either, depending on context.

The Latin present tense often covers both:

• simple present: leaves
• progressive present: is leaving

In a sentence like this, English usually translates it as leaves:

• The mother leaves the knife under the table, so that the child may not get it.

But the exact nuance depends on context.

Yes. A more literal translation of ne infans eum capiat would be:

• lest the child seize it
• so that the child may not take it

Depending on context, capiat could be translated as take, grab, seize, or get.

So several English versions are possible. The grammar stays the same: it is still a negative purpose clause introduced by ne with the subjunctive.