Мне непонятно это правило.

This rule is unclear to me.

Breakdown of Мне непонятно это правило.

• это: this
• мне: me
• правило: the rule
• непонятно: not clear

Questions & Answers about Мне непонятно это правило.

Why is it мне and not я?

Мне is the dative form of я (“I”).

Russian very often uses the dative case to show the person who experiences a state:

• Мне холодно. – I am cold. (literally: To me it is cold.)
• Мне скучно. – I am bored. (literally: To me it is boring.)

Similarly:

• Мне непонятно это правило. – I don’t understand this rule. / This rule is not clear to me.
  (literally: To me this rule is not-understandable.)

So Russian says “To me it is unclear,” using мне (dative), instead of “I” as a grammatical subject.

What exactly is непонятно? Is it an adjective, an adverb, or something else?

Formally it comes from the adjective непонятный (“unclear, not understandable”), but in this sentence непонятно is used as a predicative (a special short form used as the main part of the predicate).

Dictionaries usually label such words as “категория состояния” (category of state) or “predicative adverbs”. You meet them a lot in impersonal sentences:

• Мне понятно. – It is clear to me.
• Ему трудно. – It is hard for him.
• Нам интересно. – It is interesting to us.

So in Мне непонятно это правило, непонятно is the word that says what the situation is (it is “unclear / not understandable”).

Why is непонятно in the neuter form?

Predicative forms like понятно / непонятно, ясно, темно, скучно, холодно almost always appear in the neuter singular when they describe a general state:

• Мне холодно.
• Ей ясно.
• Им непонятно.

Here that neuter form is just the standard shape of the predicate in such impersonal or semi‑impersonal constructions.

Also, the logical subject это правило is neuter singular (правило is a neuter noun), so neuter непонятно fits naturally with it, as in:

• Это правило непонятно. – This rule is unclear.

Is это правило the subject or the object in this sentence?

Grammatically, это правило is in the nominative and functions as the subject of the sentence.

The structure is closer to:

• Это правило мне непонятно. – This rule is unclear to me.

Even though the English translation is often “I don’t understand this rule” (where “this rule” is the object), in Russian the rule is what “is unclear”, so it’s the subject, and мне is the dative “to me” (the experiencer).

Can I also say Мне это правило непонятно or Это правило мне непонятно? Are they different?

All of these are grammatically correct:

1. Мне непонятно это правило.
2. Мне это правило непонятно.
3. Это правило мне непонятно.

The difference is mainly emphasis / information structure:

• Мне непонятно это правило. – Starts from your feeling (“To me it’s unclear… which rule? This one.”).
• Мне это правило непонятно. – Keeps мне at the start and puts это правило in the middle; neutral, quite natural.
• Это правило мне непонятно. – Starts with the rule; emphasizes the rule as the topic (“This rule, specifically, is unclear to me”).

In everyday speech, Мне это правило непонятно and Это правило мне непонятно are probably the most natural-sounding.

What is the difference between Мне непонятно это правило and Я не понимаю это правило?

Both mean that you don’t understand the rule, but the nuance is different:

• Я не понимаю это правило.

  • Direct, personal, active: I do not understand this rule.
  • Focus on you and your act of understanding (or failing to understand).

• Мне непонятно это правило.

  • More impersonal / descriptive: This rule is unclear to me.
  • Focus on the rule as being difficult or unclear, rather than on you failing.

In many contexts they’re interchangeable, but:

• Talking about your own weakness or lack of knowledge → Я не понимаю это правило.
• Talking about the rule being confusing by nature → Мне (это правило) непонятно.

Can непонятно be written as two words: не понятно?

In this sentence, the standard and recommended spelling is непонятно (one word).

Writing не понятно (two words) is sometimes seen, but it can sound like you are stressing the negation (“it is not clear”) rather than stating a neutral quality (“it is unclear”). For learners, it is safer and more correct here to write:

• ✅ Мне непонятно это правило.

How would I say this in the past or future: “This rule was unclear to me / will be unclear to me”?

You keep непонятно unchanged and change the verb быть:

• Прошедшее (past):

  • Мне было непонятно это правило. – This rule was unclear to me.

• Будущее (future):

  • Мне будет непонятно это правило. – This rule will be unclear to me.

So the pattern is:

• Мне [form of быть] непонятно это правило.

Do I always need a dative like мне with непонятно?

No, but it’s very common.

You can use непонятно:

1. With a dative experiencer (who finds it unclear):

   • Мне непонятно. – It is unclear to me.
   • Им было непонятно. – It was unclear to them.

2. Without an explicit experiencer, just stating that something is unclear in general:

   • Непонятно, что он хочет. – It’s unclear what he wants.
   • Непонятно это правило. – This rule is unclear (rather bookish / less common than with dative, but possible).

In everyday speech, using the dative (мне / ему / им) is very typical when you want to say “X is unclear to me/him/them”.

Is Мне непонятно это правило an impersonal sentence?

It’s often treated as semi‑impersonal.

• There is a clear nominative это правило, which behaves like a subject.
• But the core structure “мне непонятно” is of the impersonal type (like мне холодно, мне скучно), where the state is presented without a typical personal subject (“I, you,” etc.).

From a learner’s point of view, it’s useful to see it as built from a very common pattern:

• Мне + [predicative] = “I feel / experience X”
  → Мне непонятно = It is unclear to me
  → Then you specify what is unclear: это правило.