Learn Hardcore Portuguese (Brazil): Se eu morasse perto do mar, eu caminharia na praia e não seria tão sério. - If I lived near the sea, I would walk on the beach and would not be so serious.

Se + imperfect subjunctive, conditional
- Se eu morasse perto do mar, eu caminharia na praia.
- Se eu fosse rico, eu viajaria mais.
- Se ela estudasse mais, ela passaria no exame.

So:

Se eu morasse = If I lived (but I don’t / I probably won’t)
Se eu moro = If I live (real, general condition; different meaning)
Se eu moraria = wrong; you don’t use the conditional after se in this structure.

The se‑clause uses the subjunctive, and the result clause uses the conditional.

Why are caminharia and seria used instead of simple future forms like caminharei or serei?

Caminharia and seria are in the conditional tense, used to express would + verb in English:

caminharia = would walk
seria = would be

In a hypothetical sentence with se (when the condition is unreal or unlikely), Portuguese typically does:

Se + imperfect subjunctive, conditional
- Se eu morasse perto do mar, eu caminharia na praia e não seria tão sério.
- If I lived near the sea, I *would walk on the beach and wouldn’t be so serious.*

If you used the simple future caminharei / serei, it would sound like a real, expected future result, not a purely hypothetical one, and it would be ungrammatical in this pattern:

✗ Se eu morasse perto do mar, eu caminharei na praia. (wrong combination)

So here, the conditional is the correct and natural choice.

Do I really need to repeat eu in eu caminharia and (eu) não seria tão sério?

No, you don’t need to repeat eu. Brazilian Portuguese often omits subject pronouns when the verb form already makes the subject clear.

All of these are grammatically correct:

Se eu morasse perto do mar, eu caminharia na praia e não seria tão sério.
Se eu morasse perto do mar, caminharia na praia e não seria tão sério.
Se morasse perto do mar, caminharia na praia e não seria tão sério. (more context‑dependent, but possible)

Repeating eu can add a tiny bit of emphasis or just feel natural in speech, but it’s not required. In writing, many Brazilians would actually prefer to drop the second eu:

Se eu morasse perto do mar, caminharia na praia e não seria tão sério.

Why is it perto do mar and not perto da mar or something with praia?

A few points here:

Gender of the noun
- o mar = the sea (masculine)
- a praia = the beach (feminine)
Contraction with the article
Perto de + o mar → perto do mar
- de + o = do
  That’s why you say perto do mar (near the sea), not perto de o mar or perto da mar.
Why not use praia here?
You could say perto da praia (near the beach), but it’s a slightly different image:
- perto do mar: near the sea/ocean in general (maybe sea view, coast, etc.)
- perto da praia: near the beach specifically (the sandy area where people walk, sunbathe, etc.)

Both are correct, just with different nuances. The original sentence chose mar, but Se eu morasse perto da praia… is also natural.

Why is it na praia and not à praia, da praia, or pela praia?

Na praia is a contraction of em + a praia, and em is the usual preposition for being in/on a place:

na praia = on the beach / at the beach

With caminhar (to walk), caminhar na praia means to walk on the beach (on the sand, along the beach).

Other prepositions would change the meaning:

à praia (a + a praia)
Usually means to the beach, expressing movement toward the beach:
- Vou à praia. = I am going to the beach.
  It doesn’t work with caminharia here, because we want to describe where the walking happens, not where you’re going.
pela praia (por + a praia)
Roughly along the beach / through the beach.
- Caminharia pela praia is also correct and common; it emphasizes the idea of walking along the beach.
da praia (de + a praia)
Usually means from the beach or of the beach. It wouldn’t fit well with caminharia in this sentence.

So, caminharia na praia = I would walk on the beach, which is exactly what you want here.

Could I say Se eu vivesse perto do mar instead of Se eu morasse perto do mar? Is there a difference between morar and viver?

Yes, you can say Se eu vivesse perto do mar, and it’s grammatically correct.

Basic difference:

morar = to reside / to live (somewhere), emphasizing the address or place of residence
viver = to live (broader sense: to be alive, to experience life, and sometimes to live somewhere)

In practice:

Se eu morasse perto do mar…
Focus on where you live / your residence.
Se eu vivesse perto do mar…
Still understandable as living there, but it can sound a bit more existential or broad (the life you’d have there), depending on context.

For talking specifically about where you live, morar is the most straightforward and typical verb.

What does tão sério express exactly, and how is it different from muito sério?

Both tão and muito are intensifiers, but they’re used a bit differently:

muito sério = very serious
Just states a high degree of seriousness.
tão sério = so serious
Implies comparison or contrast, often to some unstated standard or situation.

In não seria tão sério, there is a sense of “not as serious as now / as I currently am” or “not so serious (as I am in this life)”. There’s an implied comparison with the current reality.

You could also say:

… e não seria tão sério assim. = … and I wouldn’t be so serious like this.
… e não seria muito sério. = … and I wouldn’t be very serious. (still fine, but loses the comparative/contrastive feel a bit)

So tão sério fits nicely with this hypothetical “different version of me” compared to how I am now.

Can I use the present tense instead, like Se eu moro perto do mar, eu caminho na praia? How does that change the meaning?

Yes, that’s a different, but correct structure:

Se eu moro perto do mar, eu caminho na praia.

This uses:

Se + present indicative, present indicative

It expresses a real, general condition or habit:

If I live near the sea (whenever that’s the case), I walk on the beach.

It suggests something that actually happens or is seen as possible/typical, not a purely imaginary scenario.

By contrast, the original:

Se eu morasse perto do mar, eu caminharia na praia…

marks the situation as hypothetical / unreal. It implies I do not, in fact, live near the sea.

Is the comma after Se eu morasse perto do mar always necessary? Could I change the order of the clauses?

When the se‑clause comes first, you normally use a comma:

Se eu morasse perto do mar, eu caminharia na praia…

You can definitely invert the order:

Eu caminharia na praia e não seria tão sério se eu morasse perto do mar.

In this case (main clause first), the comma before the se‑clause is optional and often omitted in everyday writing:

Eu caminharia na praia e não seria tão sério se eu morasse perto do mar. (very common)
Eu caminharia na praia e não seria tão sério, se eu morasse perto do mar. (also possible, slightly more formal / marked)

So:

Se‑clause first → comma is standard.
Main clause first → comma before se is optional and more stylistic.