Learn Hardcore Russian: Учить новые слова сложнее, чем повторять старые. - Learning new words is harder than repeating old ones.

учить (что?) – “to learn / to study / to memorize” something specific (takes a direct object in the accusative).
- учить слова, учить правила, учить стихотворение
учиться (где? как? чему?) – “to study / to be a student / to learn (how to do something)”; focuses on the process of studying, not a specific object.
- учиться в школе – to study at school
- учиться плавать – to learn to swim
изучать (что?) – “to study (in depth), to research, to examine carefully.” More serious, systematic study.
- изучать язык, изучать историю
выучить (что?) – perfective of учить in the sense “to learn/memorize completely, to know by heart.”
- выучить слова – to learn the words (finish learning them)

In Учить новые слова сложнее…, the focus is on the general activity/process of learning new words (not on finishing or mastering them), so the imperfective verb учить is appropriate.

Why are новые слова in the accusative case here?

The verb учить (in the sense “to learn / memorize”) takes a direct object in the accusative case:

учить что? – слова, правила, тексты, etc.

So:

учить новые слова
- новые – accusative plural feminine/masculine-inanimate form of новый
- слова – accusative plural of слово

Since these are inanimate, their accusative plural form looks the same as the nominative plural, but grammatically they function as the direct object of учить.

Why is it сложнее and not something like более сложно? What is the difference?

Сложнее is the synthetic comparative form of the adjective сложный (“complex, difficult”). It means “more difficult / harder”.

Russian has two main ways to form the comparative:

Synthetic form (short form):
- сложный → сложнее
- трудный → труднее
- быстрый → быстрее
Analytic form with более (+ adverb/adjective):
- более сложно – more difficult
- более трудный – more difficult (adjective before noun)

In this sentence, сложнее is perfectly normal and stylistically neutral.

Учить новые слова сложнее… – standard, natural.
Учить новые слова более сложно… – grammatically possible but sounds heavier and more bookish, and is less idiomatic in this simple comparative.

Also, note nuance:

сложный – “complex, complicated” (may imply complexity, structure)
трудный – “hard, difficult” (emphasizes effort)

You could also say:

Учить новые слова труднее, чем повторять старые.

Both are correct; сложнее adds a shade of “more complex” rather than just “more effortful.”

Why is there a comma before чем? In English we don’t write “harder, than…”.

In Russian, the comma before чем in a comparison is often required when:

The comparative form (сложнее) is not directly next to the word it compares to, or
The comparison clause is more “independent” in structure.

So:

Учить новые слова сложнее, чем повторять старые. – with comma (standard spelling).

Compare with a very tight comparison, where the comma can be omitted:

Он старше меня. – “He is older than me.” (no чем, no comma)
Он умнее, чем я. – “He is smarter than I am.” (here чем usually takes a comma)

In your sentence, the structure is:
[Учить новые слова] [сложнее], чем [повторять старые].
Two infinitive phrases are being compared, so we clearly mark the boundary with a comma.

Why is повторять (imperfective) used, not повторить (perfective)?

The sentence talks about a general comparison of activities:

learning new words (in general)
reviewing old ones (in general)

For general truths, habitual actions, or ongoing processes, Russian prefers the imperfective aspect:

Учить новые слова (обычно) сложнее, чем повторять старые.

Using повторить (perfective) would imply a single, completed act of repetition:

сложнее, чем повторить старые – would suggest something like “harder than (to) repeat the old ones once / to finish repeating them,” which doesn’t match the intended general statement.

So imperfective повторять is the natural choice for describing a repeated or habitual action being compared.

Why does the sentence end with just старые and not старые слова?

Russian often drops a repeated noun when it is clear from context, leaving only the adjective:

Учить новые слова сложнее, чем повторять старые (слова).

Here старые is a shortened noun phrase: it means “old ones”, with слова understood from the earlier phrase новые слова.

This is very common and natural:

Я люблю старые книги, а не новые. – “I like old books, not new ones.”
Свежее молоко полезнее, чем старое. – “Fresh milk is healthier than old (milk).”

So repeating слова would be grammatically fine but a bit heavier and less natural in a short sentence.

Can we change the word order to Сложнее учить новые слова, чем повторять старые? Does it change the meaning?

Yes, that word order is correct:

Сложнее учить новые слова, чем повторять старые.

The basic meaning stays the same. The difference is one of emphasis and rhythm:

Учить новые слова сложнее, чем повторять старые.
Slightly more neutral, topic-first: “As for learning new words – it is harder than reviewing old ones.”
Сложнее учить новые слова, чем повторять старые.
Slightly more focus on the difficulty itself: “It is harder to learn new words than to review old ones.”

Both are natural in speech and writing.

Is чем here a preposition or a conjunction, and is it always used with comparatives like this?

In this sentence, чем functions as a subordinating conjunction introducing a comparative clause:

сложнее, чем повторять старые – “harder than (to) review the old ones”

Some points:

With comparative forms like лучше, хуже, сложнее, легче, быстрее, медленнее, чем is the normal way to introduce the thing you are comparing to:
- Легче читать, чем писать. – It’s easier to read than to write.
- Интереснее смотреть фильм, чем читать книгу.
Sometimes you can omit “чем” and the clause entirely if it’s understood:
- Учить новые слова сложнее. – “Learning new words is harder.” (than something else, implied)
When you compare nouns directly, sometimes чем is dropped and you use cases instead:
- Он старше меня. – “He is older than me.” (no чем)

But in your construction (comparing two infinitive phrases), using чем is standard and needed.

Could we replace учить with изучать or выучить in this sentence? How would that change the nuance?

If you change the verb, the nuance shifts:

Изучать новые слова сложнее, чем повторять старые.
- изучать suggests more systematic, in-depth study, like analyzing usage, etymology, contexts.
- Sounds more formal and a bit unusual specifically with слова; more natural with язык, тему, предмет:
  - Изучать язык сложнее, чем повторять слова.
Выучить новые слова сложнее, чем повторять старые.
- выучить is perfective: to finish learning / to learn completely.
- This would mean “It is harder to fully learn/master new words than to review old ones.”
- Grammatically correct, but the sentence now compares completed mastery of new words with the ongoing activity of reviewing old words — a slightly mixed comparison. More symmetrical would be:
  - Выучить новые слова сложнее, чем выучить старые.

The original Учить новые слова… neatly captures the general ongoing activity, which is why it is the most natural choice here.