Cette vieille chaise est moins solide que le fauteuil.

Cette is the feminine singular form of the demonstrative adjective meaning this or that. Since chaise is a feminine singular noun, French uses cette.

The main forms are:

• ce
  • masculine singular noun before a consonant
• cet
  • masculine singular noun before a vowel or silent h
• cette
  • feminine singular noun
• ces
  • plural noun

So:

• ce fauteuil
• cette chaise

Some French adjectives usually come before the noun, and vieux/vieille is one of them. It belongs to a common group of adjectives often placed before the noun, especially adjectives of age, size, beauty, and goodness.

So une vieille chaise is the normal order.

If you put vieille after the noun, it would usually sound unusual here or give a different effect.

Yes. French adjectives must agree with the noun they describe in gender and number.

Since chaise is feminine singular, vieux changes to vieille.

Compare:

• un vieux fauteuil
• une vieille chaise
• de vieux fauteuils
• de vieilles chaises

Because solide is an adjective. With adjectives, French uses:

moins + adjective

So:

• moins solide = less solid
• plus solide = more solid
• aussi solide = as solid

You use moins de before a noun, not an adjective:

• moins de bois = less wood

Moins ... que is the standard French pattern for less ... than.

The structure is:

moins + adjective/adverb + que

So:

• moins solide que le fauteuil = less solid than the armchair

Related comparison patterns:

• plus ... que = more ... than
• aussi ... que = as ... as

Here que means than. It introduces the second part of the comparison.

So the sentence compares:

• cette vieille chaise with
• le fauteuil

In this sentence, que is not a relative pronoun. It is simply the comparison word than.

Before a vowel sound, que becomes qu':

• moins élégant qu'un canapé

Le is the definite article, so it refers to a specific armchair that is already known from the context.

French often uses the definite article when both speaker and listener know which thing is being talked about.

If you said un fauteuil, it would mean an armchair, which sounds less specific. Both can be grammatical, but they do not mean exactly the same thing.

Because the subject is already clearly stated: cette vieille chaise.

When French has a normal subject noun phrase, it usually uses the regular form of être:

• Cette vieille chaise est moins solide...

C'est is used in other kinds of sentences, often to identify or present something:

• C'est une vieille chaise.

So in this sentence, est is the normal choice.

Yes, it does, but you do not see a visible change here. Solide has the same form in masculine and feminine singular.

Compare:

• un fauteuil solide
• une chaise solide

In the plural, it changes to solides:

• des fauteuils solides
• des chaises solides

A careful approximation is:

set vyey shez eh mwan so-leed kuh luh fo-tuy

A more precise IPA pronunciation is:

/sɛt vjɛj ʃɛz ɛ mwɛ̃ sɔ.lid kə lə fo.tœj/

A few helpful points:

• cette sounds like set
• vieille is roughly vyey
• chaise sounds like shez
• the s in moins is normally silent here
• fauteuil ends with a vowel sound that does not exist exactly in English, so fo-tuy is only an approximation