Learn Hardcore Russian: Разумеется, нельзя забывать проверять значение каждого нового слова. - Of course, one must not forget to check the meaning of each new word.

Разумеется means of course or naturally. It emphasizes that something is self-evident or goes without saying. Конечно also means of course, but it is more neutral and common in everyday speech; разумеется is slightly more formal or emphatic.

Why is there a comma after Разумеется?

Because Разумеется is an introductory word (a parenthetical). In Russian, such words are separated from the main clause by a comma.

What does нельзя mean here, and how is it different from нужно or надо?

Нельзя literally means it is not allowed, but with an infinitive it often expresses a strong recommendation or obligation: one must not forget, i.e., you absolutely must not fail to. Нужно/надо simply mean it is necessary or you need to, which is softer and lacks the prohibitive nuance.

Why is забывать in the infinitive?

After impersonal modal words like нельзя, Russian uses the infinitive to express the prohibited or required action. There’s no personal subject, so “забывать” generalizes “one must not forget.”

Why are there two infinitives in a row (забывать проверять)?

The verb забывать takes another infinitive as its complement when you mean forget to do something. So нельзя забывать (you must not forget) governs проверять (to check), which describes what must not be forgotten.

What case is значение, and why?

Значение is in the accusative singular because it’s the direct object of проверять. For inanimate nouns like значение, the accusative singular form is identical to the nominative.

What is the case of каждого нового слова, and why is it singular?

Каждого нового слова is genitive singular. The genitive here indicates “the meaning of each new word” (a partitive/genitive attribute), and singular is used because we refer to each individual word’s meaning one at a time. Новогo agrees in gender, number, and case with слова.

Could we use нужно or надо instead of нельзя, and what would change?

Yes. Нужно забывать проверять or Надо забывать проверять would mean you need to remember to check, sounding softer and more neutral. Using нельзя adds a stronger, almost prohibitive or obligatory nuance (you absolutely must not forget).

Why use значение rather than перевод in this context?

Значение means meaning (the definition or sense of a word), while перевод means translation (the specific equivalent in another language). Checking the значение implies consulting a dictionary for the full definition, not just finding a one-to-one equivalent.