O ribeiro passa pelo vale.

O is the masculine singular definite article, meaning the.

So o ribeiro = the stream / the brook.

Portuguese uses the definite article more regularly than English does. In a simple statement like this, using o is completely normal if you are talking about a specific stream or about the stream in that landscape.

Not exactly.

• ribeiro usually means stream, brook, or small river
• rio means river

So ribeiro suggests something smaller than a rio.

Also, ribeiro is a masculine noun, which is why it takes o:

• o ribeiro
• not a ribeiro

Passa is the 3rd person singular of the verb passar in the present indicative.

Here are a few forms of passar:

• eu passo
• tu passas
• ele/ela/você passa
• nós passamos
• eles/elas/vocês passam

Because the subject is o ribeiro (the stream), Portuguese uses passa:

• O ribeiro passa pelo vale.
• The stream passes through the valley.

Because in Portuguese, por + o contracts to pelo.

So:

• por + o = pelo
• por + a = pela
• por + os = pelos
• por + as = pelas

That means:

• pelo vale = through the valley / by the valley

You normally would not say por o vale in standard Portuguese.

It can mean either, depending on context.

With a place like vale (valley), passa pelo vale will often be understood as:

• goes through the valley
• runs through the valley

For a stream, English often prefers runs through:

• The stream runs through the valley.

But grammatically, Portuguese is using passar por.

Because Portuguese usually uses an article with a noun like this when referring to a specific place.

So:

• pelo vale = through the valley

Without the article, por vale would sound incomplete or unnatural in this sentence.

This is another place where Portuguese often uses articles more than English does.

Yes, Portuguese word order is fairly flexible.

The neutral, most straightforward order is:

• O ribeiro passa pelo vale.

But you can also say:

• Pelo vale passa o ribeiro.

That version sounds more literary, descriptive, or focused on pelo vale.

So both are possible, but the original sentence is the most neutral and standard.

Not exactly. In European Portuguese, unstressed vowels are often reduced.

A learner-friendly approximation of the whole sentence is:

• O ribeiro passa pelo vale
• roughly: u ribÊIru PASSA pelu VA-l(ə)

A few useful pronunciation notes:

• o by itself is often pronounced more like u
• ei in ribeiro sounds like ay
• unstressed e often becomes a very reduced sound in European Portuguese
• the r at the start of ribeiro is a stronger Portuguese r

You do not need perfect pronunciation at first, but it helps to know that European Portuguese often sounds more reduced than Brazilian Portuguese.

Yes, in many contexts you could.

• O ribeiro passa pelo vale.
• O ribeiro atravessa o vale.

Both can suggest that the stream goes through the valley.

But there is a slight difference:

• passa pelo vale = more general: passes through / goes through the valley
• atravessa o vale = more directly crosses the valley

So atravessa can sound a bit more explicit about crossing from one side to another.

Because Portuguese normally does not need a subject pronoun when the subject is already expressed as a noun.

So:

• O ribeiro passa pelo vale.

is complete by itself.

You would not normally say:

• O ribeiro ele passa pelo vale.

That sounds unnecessary here.

Portuguese often leaves pronouns out unless they are needed for emphasis, contrast, or clarity.