Ianua firma est, et ventus eam aperire non potest.

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

In Ianua firma est:

• ianua = door
• firma = strong / sturdy / firm
• est = is

So ianua is the thing being described, which makes it the subject.

Also, ianua is a first-declension feminine noun, so that helps explain why the adjective is feminine too.

Firma agrees with ianua.

In Latin, adjectives usually match the nouns they describe in:

• gender
• number
• case

Since ianua is:

• feminine
• singular
• nominative

the adjective must also be:

• feminine
• singular
• nominative

So we get firma.

This is a good example of a predicate adjective: the adjective is linked to the noun by est rather than sitting directly beside it in an attributive phrase.

Est is the third-person singular present form of esse, meaning to be.

So firma est means is strong.

Latin often uses esse the same way English uses to be:

• Puella laeta est = The girl is happy
• Ianua firma est = The door is strong

Latin does not have definite or indefinite articles like English the, a, or an.

So:

• ianua can mean door, a door, or the door
• ventus can mean wind, a wind, or the wind

You figure out which is best from context.

That is very normal in Latin, and English speakers often need time to get used to it.

Because ventus is in the nominative singular, just like ianua was in the first clause.

In et ventus eam aperire non potest:

• ventus = the wind
• eam = her / it (here, it, referring to the door)
• aperire = to open
• non potest = cannot

So ventus is the thing doing the action, which makes it the subject.

Eam is the accusative singular feminine form of the pronoun is, ea, id.

Here it means it, referring back to ianua.

It is feminine because ianua is feminine, and it is accusative because it is the direct object of aperire:

• the wind cannot open it

So:

• ea = nominative feminine singular
• eam = accusative feminine singular

English does something similar with she / her or he / him, but Latin marks this more systematically.

It could repeat the noun, but using a pronoun is very natural when the reference is already clear.

So Latin can say:

• ventus ianuam aperire non potest
• ventus eam aperire non potest

Both are possible, but eam avoids repeating ianua.

This works much like English using it instead of saying the door again.

Because after potest Latin normally uses an infinitive.

Potest means is able or can, and the infinitive gives the action that someone is able to do.

So:

• aperire potest = can open
• literally, is able to open

This is very similar to English:

• He can run
• She can see
• The wind cannot open it

In Latin, the verb after potest is not a finite verb; it stays in the infinitive.

Because non negates the verb phrase, and in this sentence it is negating potest:

• non potest = cannot / is not able

That is the normal way to say cannot in Latin.

Latin word order is flexible, so you may sometimes see potest non... in other contexts, but that can have a different nuance, more like is able not to... or can refrain from...

Here, aperire non potest clearly means cannot open.

Latin word order is much freer than English word order because the endings show what each word is doing.

So all of these are understandable Latin in principle:

• ventus eam aperire non potest
• ventus non potest eam aperire
• eam ventus aperire non potest

The form eam is accusative, so you can still tell it is the object even when it is not right after the verb.

English relies much more on word order, while Latin relies much more on case endings.

Et means and, and it joins the two clauses:

• Ianua firma est
• ventus eam aperire non potest

So the full sentence contains two linked ideas:

1. the door is strong
2. the wind cannot open it

This is a very common and straightforward use of et.

Here it means something like strong, solid, or sturdy in a physical sense.

Because the subject is ianua (door), the adjective is naturally understood as describing physical strength or solidity, not personality or moral character.

Context is what tells you which shade of meaning is intended.

Grammatically, yes: eam can mean her or it, depending on what noun it refers to.

But in this sentence it refers back to ianua, which is a feminine noun meaning door. Since English uses it for objects like a door, the best translation is it.

This is something English speakers often notice: Latin grammatical gender does not always match natural gender in English. A thing can be grammatically feminine, masculine, or neuter without being biologically female, male, or neither.

It has two main clauses joined by et:

Clause 1:
Ianua firma est

• subject: ianua
• predicate adjective: firma
• verb: est

Clause 2:
ventus eam aperire non potest

• subject: ventus
• object: eam
• infinitive: aperire
• finite verb: potest
• negation: non

So the sentence shows two very common Latin patterns:

• subject + predicate adjective + est
• subject + object + infinitive + non potest