Si stabulum bene clausum erit, nullus bos nocte exibit.

Because Latin often uses the future perfect in an if clause when the action must be completed before the main future action happens.

So:

Si stabulum bene clausum erit, nullus bos nocte exibit.

literally means something like:

If the stable will have been well shut, no ox will go out at night.

In natural English, we usually say:

If the stable is well shut...
or
If the stable has been well shut...

So this is a very normal Latin pattern: future perfect in the si clause, and future in the main clause.

It is a two-word verb form.

• clausum = the perfect passive participle of claudere
• erit = future of esse

Together they form the future perfect passive indicative:

clausum erit = will have been shut / closed

So even though it is written as two words, it functions as one verbal idea.

Because clausum agrees with stabulum.

• stabulum is neuter
• singular
• nominative

So the participle must match it:

• masculine singular: clausus
• feminine singular: clausa
• neuter singular: clausum

Since the subject is stabulum, the correct form is clausum.

It is nominative singular.

Even though English says the stable is shut, Latin still treats stabulum as the subject of the passive verb:

stabulum ... clausum erit = the stable will have been shut

So stabulum is the thing that will have been shut, and that makes it the subject.

Nullus bos means not a single ox.

Latin often uses a singular noun with nullus to give a strong sense of not one.

So:

• nullus bos = no ox, not a single ox
• nulli boves = no oxen

Both could make sense in different contexts, but the singular here is perfectly natural and slightly more pointed.

Also, nullus agrees with bos:

• both are nominative singular masculine

Nocte is ablative singular of nox, noctis.

Here it is an ablative of time when, meaning at night.

Latin often uses the ablative without a preposition for expressions of time:

• nocte = at night
• aestate = in summer
• eo die = on that day

So nocte exibit means he/it will go out at night.

Exibit is future active indicative, third person singular.

It comes from exire, meaning to go out.

So:

• exibit = he/she/it will go out

Since the subject is bos, it means:

the ox will go out

or with nullus:

no ox will go out

Because Latin does not have articles like English the and a/an.

So stabulum can mean:

• a stable
• the stable

The context tells you which English article to use.

That is why stabulum bene clausum erit can be translated naturally as if the stable is well shut, even though there is no separate Latin word for the.

The word order is meaningful, but Latin is much more flexible than English.

This sentence puts related words near each other:

• bene clausum keeps bene close to clausum
• nullus bos keeps the adjective and noun together
• nocte exibit places the time expression just before the verb

A different order could still mean the same thing, because the endings show the grammar. But the given order is smooth and natural.

Yes, but here bene means properly, securely, or thoroughly.

So bene clausum erit is not just closed in a good way in a vague sense. It suggests:

• properly shut
• securely closed
• well fastened

That makes good sense with the result:

if the stable is securely shut, no ox will go out

Because bos, bovis is an irregular-looking third-declension noun meaning ox or cow.

Its nominative singular is simply bos, which can seem surprising if you are expecting something like a second-declension form.

Some forms are:

• nominative singular: bos
• genitive singular: bovis
• nominative plural: boves

So in this sentence, bos is just the normal nominative singular form.