Learn Hardcore Spanish (Spain): Mi abuelo nos enseña qué mesas y sillas son de madera buena y cuáles son baratas. - My grandfather teaches us which tables and chairs are made of good wood and which are cheap.

Direct question:
¿Qué mesas y sillas son de madera buena? – Which tables and chairs are made of good wood?
Indirect question:
Mi abuelo nos enseña qué mesas y sillas son de madera buena. – My grandfather teaches us which tables and chairs are made of good wood.

If you wrote que (without accent) here, it would suggest a different structure (a relative clause) and would be ungrammatical in this sentence. The accent marks its interrogative value inside the larger sentence.

What’s the difference between qué and cuáles in this sentence?

They both roughly mean “which”, but they’re used differently:

qué is used before a noun:
- qué mesas y sillas = which tables and chairs
cuáles is used on its own, standing for a noun that is already known from context:
- cuáles (son baratas) = which (ones are cheap)

In your sentence:

First, the noun is expressed: qué mesas y sillas
Later, Spanish avoids repeating mesas y sillas, so it uses cuáles alone: cuáles son baratas = which (ones) are cheap.

So you can think:

qué + noun = “which [noun]”
cuál/cuáles (alone) = “which one / which ones”

Why is it madera buena and not buena madera? Are both possible?

Both word orders are possible, but they have slightly different flavors:

madera buena (adjective after the noun)
- More neutral, descriptive: good-quality wood in a factual way.
- Very typical, “default” word order in Spanish for most adjectives.
buena madera (adjective before the noun)
- Can sound a bit more emphatic or subjective, like “really good wood,” “nice wood.”
- Pre‑noun position often adds a touch of evaluation or emotional color.

In this sentence:

son de madera buena is natural everyday Spanish: “are made of good (quality) wood.”
son de buena madera is also possible and would often be understood the same way; the difference here is subtle and many speakers would use them almost interchangeably.

So:

de madera buena = neutral description of quality
de buena madera = also fine, sometimes a bit more evaluative/emphatic

Why is it son de madera buena and not just son madera buena?

Spanish normally uses ser + de + material for “to be made of (material)”:

La mesa es de madera. – The table is (made) of wood.
Las sillas son de metal. – The chairs are (made) of metal.

So you say:

son de madera buena – they are (made) of good wood.

If you said son madera buena, it would sound more like “they are good wood” as if the objects themselves are wood as a substance, not objects made of wood. That wording is unusual for furniture.

So:

Material of an object: ser de + material
→ son de madera buena = correct and natural here.

What exactly does nos do in Mi abuelo nos enseña…? Why is it needed?

Nos is an indirect object pronoun meaning “to us”.

enseñar = “to teach” / “to show”
Mi abuelo enseña… = “My grandfather teaches…” (but we don’t know whom he teaches)
Mi abuelo nos enseña… = “My grandfather teaches us…”

Spanish almost always uses pronouns like me, te, le, nos, os, les whenever you want to say to me, to you, to him, to us, etc., even if you could guess it from context.

So the structure is:

Mi abuelo (subject)
nos (indirect object: to us)
enseña (verb: teaches)
qué mesas y sillas… (what he teaches us: the content)

Without nos, the sentence loses who is being taught.

Why do we repeat son: son de madera buena y cuáles son baratas? Could we drop the second son?

You could drop the second son in casual speech:

…qué mesas y sillas son de madera buena y cuáles baratas.

Native speakers might say this, and it would be understood. However:

With cuáles, it’s much clearer and more natural to repeat the verb:
- cuáles son baratas is the standard, full clause.
In learner or formal Spanish, repeating son is better style, because it avoids any ambiguity or processing effort.

So:

Grammatically possible to omit the second son in fast spoken Spanish.
But cuáles son baratas is the clear, recommended form, especially in writing or for learners.

Why is there no article in qué mesas y sillas or cuáles son baratas? Could I say qué las mesas or cuáles son las baratas?

You must not use an article after qué when it directly modifies a noun:

✅ qué mesas y sillas – correct
❌ qué las mesas y las sillas – incorrect

With cuáles, both with and without article are possible, but they mean slightly different things:

cuáles son baratas
= which (ones) are cheap – general, open question.
cuáles son las baratas
= more like which ones are *the cheap ones* – assuming there is a known set/group of “cheap ones.”

In your sentence, cuáles son baratas is perfectly natural and fits the general idea of “which ones are cheap.” Adding las would still be grammatically correct, but it slightly changes the nuance to “which are the cheap ones (among them).”

Why is baratas feminine and plural?

Baratas must agree with the noun(s) it refers to in gender and number.

The implied noun here is mesas y sillas:
- mesas – feminine plural
- sillas – feminine plural
  Together they are “feminine plural” as a group in Spanish.

So:

Feminine plural adjective: baratas
→ cuáles son baratas = which (of them) are cheap (mesas y sillas).

If you changed the nouns, the adjective would change:

qué sofás y sillones son cómodos y cuáles son caros.
(masculine plural → cómodos, caros)

What’s the difference between enseñar, mostrar, and explicar here? Could I say Mi abuelo nos muestra…?

All three are related but not identical:

enseñar = to teach (also to show in some contexts)
- Suggests passing on knowledge or skills.
- Mi abuelo nos enseña qué mesas… → he is teaching us how to recognize them.
mostrar = to show
- Focus on visually pointing out or presenting something.
- Mi abuelo nos muestra qué mesas y sillas son de madera buena…
  → He points at them / demonstrates which ones they are.
explicar = to explain
- Focus on verbal explanation.
- Mi abuelo nos explica qué mesas y sillas son de madera buena…
  → He explains why or how they are good wood or cheap.

All three can fit, but:

enseñar emphasizes learning a skill or distinction (most natural here).
mostrar/ explicar change the nuance to “showing” or “explaining.”

Is there anything specifically “Spain Spanish” about this sentence?

The sentence is perfectly standard and works in both Spain and Latin America. There is no vocabulary or structure that is exclusive to Spain.

A few notes:

abuelo is used everywhere for “grandfather”; in Spain it can also be a familiar way to address an older man, but here it’s clearly “my grandfather.”
nos enseña is standard for all varieties of Spanish.
For Spain-specific differences, you’d notice things more in pronunciation (e.g. ceceo with z and c before e/i) or second-person plural forms (vosotros, os), but none of that appears in this sentence.

So this example is valid as-is for “Spanish (Spain),” and any native from Spain would say and understand it naturally.