Теперь мне яснее, почему в этом предложении нужна запятая.

Because Russian often uses the dative case to mark the person to whom something is clear, easy, difficult, interesting, and so on.

So:

• мне ясно = it is clear to me
• тебе трудно = it is difficult for you
• ему интересно = it is interesting to him

In this sentence, мне яснее literally means to me, it is clearer.

This is different from English, where we usually make I the subject: Now I understand more clearly... Russian often avoids that kind of subject and uses an impersonal-style construction instead.

Яснее is the comparative form of ясно / ясный, meaning clearer or more clearly understood.

So:

• ясно = clear
• яснее = clearer

In this sentence, Теперь мне яснее means something like:

• Now it’s clearer to me
• Now I understand more clearly

It does not necessarily mean that the sentence itself became clearer; it means the speaker’s understanding improved.

Both are possible in Russian, but яснее is the more natural and common comparative here.

Russian often prefers simple comparative forms:

• быстрее = faster
• лучше = better
• яснее = clearer

The form более ясно is grammatically possible, but it sounds more formal, heavier, or less conversational in a sentence like this.

So Теперь мне яснее... is the normal everyday choice.

Because почему в этом предложении нужна запятая is a subordinate clause.

The main clause is:

• Теперь мне яснее

The subordinate clause explains what is clearer now:

• почему в этом предложении нужна запятая

Russian normally separates subordinate clauses from the main clause with a comma.

So the structure is:

• Теперь мне яснее, почему...
• Мне понятно, что...
• Я знаю, где...

Even though in English punctuation can sometimes feel different, in Russian this comma is required.

Почему means why, and here it introduces an indirect question.

Compare:

• Direct question: Почему нужна запятая? = Why is a comma needed?
• Indirect question: Теперь мне яснее, почему нужна запятая. = Now it’s clearer to me why a comma is needed.

So почему is not asking the listener a question directly. Instead, it introduces the content of what has become clearer.

This is very common in Russian:

• Я знаю, где он живёт.
• Мне интересно, когда она придёт.
• Непонятно, как это работает.

This means in this sentence.

Breakdown:

• в = in
• этом = this, in the prepositional singular form
• предложении = sentence, in the prepositional singular form

After в when talking about location, Russian usually uses the prepositional case:

• в доме = in the house
• в книге = in the book
• в предложении = in the sentence

Since это предложение is neuter, the forms are:

• nominative: это предложение
• prepositional: в этом предложении

Because нужна agrees with запятая, and запятая is feminine singular.

Russian past tense and short-form adjectives often agree in gender and number with the noun they describe. Here нужна is the short form of нужный and means needed / necessary.

Agreement:

• нужен for masculine singular
• нужна for feminine singular
• нужно for neuter singular
• нужны for plural

So:

• нужен стол
• нужна книга
• нужно время
• нужны документы

Since запятая is feminine, it must be нужна запятая.

Because нужна запятая is a very natural way in Russian to say a comma is needed.

It is a simple statement of necessity:

• Здесь нужна запятая. = A comma is needed here.

Other expressions are possible, but they mean slightly different things:

• нужно поставить запятую = it is necessary to put a comma
• следует поставить запятую = one should put a comma (more formal)
• стоит поставить запятую = it would be worth putting a comma / it’s advisable to put a comma

So нужна запятая is straightforward and idiomatic.

Yes, it can be.

Теперь мне яснее. by itself means:

• Now it’s clearer to me
• Now I understand better

In your full sentence, the speaker then adds what has become clearer:

• Теперь мне яснее, почему...

So the second part expands the thought, but the first part can stand on its own in context.

Yes, absolutely. That is a very natural alternative.

Compare:

• Теперь мне яснее, почему...
• Теперь я лучше понимаю, почему...

They are close in meaning, but the nuance is slightly different:

• мне яснее sounds a bit more like it has become clearer to me
• я лучше понимаю sounds more directly like I understand better

Both are good Russian. The version with мне яснее is slightly more impersonal and often feels elegant and natural in explanations.

Because Russian often leaves out dummy subjects like English it.

English says:

• It is clear to me
• It is easier
• It is interesting

Russian usually just says:

• Мне ясно
• Мне легче
• Мне интересно

So Теперь мне яснее literally looks like Now to me clearer, but in real English we translate it as Now it’s clearer to me or Now I understand more clearly.

This is a very common Russian pattern.

Yes. Words like ясно, понятно, известно, интересно, and their comparative forms can introduce a clause explaining the content.

For example:

• Мне ясно, что он прав.
• Теперь понятно, почему он ушёл.
• Стало известно, где они живут.
• Мне интереснее, как это работает.

So Теперь мне яснее, почему... is a normal structure: a predicative word plus a subordinate clause.

The sentence has two parts:

1. Main clause:

   • Теперь мне яснее
   • Now it’s clearer to me

2. Subordinate clause:

   • почему в этом предложении нужна запятая
   • why a comma is needed in this sentence

So the full structure is:

• Now it’s clearer to me + why a comma is needed in this sentence

This kind of structure is very common in Russian when talking about knowing, understanding, remembering, noticing, or explaining something.