Haec sententia difficilior est quam illa.

Because haec has to agree with sententia.

• sententia is feminine
• sententia is singular
• here it is nominative, because it is the subject

So the demonstrative meaning this must also be feminine singular nominative: haec.

A learner may notice that haec can also be neuter plural nominative/accusative, but in this sentence it is clearly feminine singular because it goes with sententia.

Sententia is nominative singular.

You can tell this because:

• it is the thing being talked about, so it is the subject
• the verb is est = is
• the sentence says that this sentence is something: more difficult than that one

So haec sententia is the subject, and both words are nominative singular feminine.

Because difficilior is the comparative form of difficilis.

• difficilis = difficult
• difficilior = more difficult

Latin often forms the comparative by adding -ior (or -ius in the neuter).

In this sentence, difficilior is nominative singular and agrees with sententia. For masculine and feminine nominative singular, the comparative form is the same: -ior.

Because comparative adjectives in Latin work a little differently from many other adjectives.

For the comparative:

• masculine singular nominative = -ior
• feminine singular nominative = -ior
• neuter singular nominative = -ius

So even though sententia is feminine, the correct form is still difficilior, not something like difficiliora.

Quam means than in a comparison.

So:

• difficilior = more difficult
• quam illa = than that one

Latin commonly uses comparative adjective + quam to compare two things directly.

In this sentence, haec sententia is being compared with illa.

Because Latin often leaves out a noun when it is obvious from context.

So illa here means:

• that one
• or more fully, that sentence

The noun sententia is understood and does not need to be repeated. This is very common in Latin and in English too. Compare English This sentence is harder than that one, where sentence is also omitted after that.

Illa is nominative singular feminine.

That may seem surprising at first, because in English than that one does not feel like a subject. But in Latin, with quam after a comparative, the second thing compared is often put in the same case as the first.

So:

• haec sententia = nominative singular feminine
• illa = nominative singular feminine, with sententia understood

In other words, Latin is comparing this sentence with that sentence directly.

Yes. Latin agreement does not depend on word order.

Difficilior agrees with sententia in:

• number: singular
• case: nominative
• gender: feminine

Even though it comes later in the sentence, it still describes sententia.

Yes, Latin can sometimes leave out est when the meaning is clear, especially in poetry or very compressed styles. But in normal prose, including est is completely natural.

So:

• Haec sententia difficilior quam illa could be understood
• but Haec sententia difficilior est quam illa is clearer and more standard for a learner

Here est simply links the subject with the comparative adjective.

The word order is natural, but Latin word order is more flexible than English word order.

This sentence is arranged as:

• Haec sententia = this sentence
• difficilior est = is more difficult
• quam illa = than that one

That is a very straightforward order. But Latin could rearrange parts of the sentence for emphasis. The endings, not the position alone, tell you how the words relate to each other.

Yes. Latin sometimes uses the ablative of comparison instead of quam.

For example, with a noun, Latin can say something like This sentence is more difficult than that sentence either with quam or with an ablative comparison.

However, with pronouns such as illa, Latin very often prefers quam, because it is clearer and more natural. So quam illa is exactly what a learner should expect here.

No. Sententia can have several meanings depending on context, including:

• sentence
• opinion
• view
• judgment
• thought

In this particular sentence, it means sentence, but a learner should know that the word is broader than the English word sentence alone.