Эта диета кажется сложной, но полезной.

This diet seems difficult but useful.

Breakdown of Эта диета кажется сложной, но полезной.

• но: but
• полезный: useful
• сложный: difficult
• эта: this
• казаться: to seem
• диета: the diet

Questions & Answers about Эта диета кажется сложной, но полезной.

Why is it эта диета and not эту диету at the beginning?

Because эта диета is the subject of the sentence, so it must be in the nominative case.

• эта – nominative feminine singular demonstrative pronoun (this)
• диета – nominative feminine singular noun (diet)

The verb кажется here behaves like “to be / to seem” in English. The thing that seems is the subject:

• Эта диета кажется... – This diet seems...

If you used эту диету (accusative), it would normally be the object of some action, for example:

• Я начинаю эту диету. – I’m starting this diet.

But in our sentence, nothing is being done to the diet; the diet itself seems a certain way, so nominative is correct: эта диета.

Why are сложной and полезной in that form? Why not just сложная, но полезная?

Сложной and полезной are in the instrumental case, feminine singular. In Russian, after verbs like:

• быть (to be) in the past/future
• стать (to become)
• казаться (to seem)
• являться (to be, to constitute)

the predicative complement (what the subject “is / becomes / seems”) is often put in the instrumental case, especially in neutral, standard written language.

So:

• Эта диета кажется сложной, но полезной.
  Literally: This diet seems (as) difficult, but beneficial.
  (adjectives in instrumental: сложной, полезной)

These agree with диета (feminine singular) in gender and number, and are in instrumental case because of кажется.

You can sometimes hear nominative in informal speech:

• Эта диета кажется сложная, но полезная.

But in standard, textbook Russian, with казаться it’s more correct and natural to use the instrumental: сложной, но полезной.

So is it always instrumental after кажется?

With казаться + adjective, instrumental is the default, standard choice, especially in careful speech and writing:

• Он кажется усталым. – He seems tired.
• Эта идея кажется странной. – This idea seems strange.

However:

• In spoken, informal Russian, you will also hear adjectives in the nominative:
  • Он кажется усталый.
  • Эта идея кажется странная.

This nominative usage is common in conversation but is considered less formal / less standard. For learners, it’s safer to stick to:

кажется + adjective in instrumental: кажется сложной, полезной, интересным etc.

What exactly is the difference between сложный and трудный? Could we say эта диета кажется трудной?

Both сложный and трудный can be translated as “difficult”, but their nuances differ:

• сложный – literally complex, complicated, with many parts or rules.
  Emphasis: structure, complexity.
• трудный – hard, challenging, requiring effort.
  Emphasis: effort, difficulty of doing it.

For a diet:

• сложная диета – the diet has a complicated structure: many rules, timings, restrictions.
• трудная диета – the diet is hard to follow: you suffer, you’re hungry, it’s hard to stick to.

Both are possible:

• Эта диета кажется сложной, но полезной. – It seems complex but beneficial.
• Эта диета кажется трудной, но полезной. – It seems hard (to follow) but beneficial.

The original sentence highlights the complicated nature of the diet, not just the effort.

What is кажется grammatically? Is it reflexive? How is it formed?

Кажется is the 3rd person singular of the imperfective verb казаться (to seem, to appear), which is indeed a reflexive verb.

• Infinitive: казаться
• Present:
  
  • я кажусь
  • ты кажешься
  • он/она/оно кажется
  • мы кажемся
  • вы кажетесь
  • они кажутся

The -ся / -сь ending marks it as reflexive. Historically, this comes from a reflexive pronoun, but in modern Russian many verbs with -ся (like казаться, нравиться, бояться) simply have special meanings and are learned as whole verbs.

In this sentence:

• кажется = (it) seems / appears

So: Эта диета кажется сложной, но полезной.
= This diet seems difficult but beneficial.

Sometimes I see Кажется, ... at the beginning of a sentence. Is that the same кажется as here?

Yes, it’s the same word, but used in a slightly different way.

1. Personal construction (like in your sentence):
   There is a clear subject.

   • Эта диета кажется сложной. – This diet seems difficult.
     Subject: эта диета

2. Impersonal / parenthetical construction:

   • Кажется, я забыл телефон. – It seems (I think) I forgot my phone.
   • Мне кажется, это ошибка. – It seems to me this is a mistake.

Here кажется acts more like a parenthetical phrase: it seems / apparently / I think. It comments on the whole clause that follows. Grammatically it’s still a verb, but functionally it’s similar to an adverb or discourse marker.

In your sentence, кажется directly links эта диета with the adjectives сложной and полезной.

Why is there a comma before но?

In Russian, но is a coordinating conjunction meaning “but”. It connects two parts that contrast with each other.

Here it connects two adjectives that describe the same noun, but with opposite or contrasting ideas:

• сложной (difficult/complex)
• полезной (useful/beneficial)

These are homogeneous parts of the predicate (both are instrumental adjectives after кажется), and Russian punctuation requires a comma before но when it introduces a contrasting element:

• …кажется сложной, но полезной.
• Он устал, но доволен.
• Это дорого, но качественно.

Could we change the word order, like Эта диета сложной кажется, но полезной?

No, Эта диета сложной кажется, но полезной sounds wrong and unnatural.

Some word order changes are possible in Russian, but:

• The standard neutral order here is:
  • Эта диета кажется сложной, но полезной.

Natural variations might be:

• Диета кажется сложной, но полезной. (dropping эта if context allows)
• Кажется, эта диета сложной, но полезной. (less natural; would usually need adjustment)

But placing кажется after сложной breaks the natural flow and expected pattern: subject – verb – complement.

So for learners, keep:

Эта диета кажется сложной, но полезной.

How do you pronounce Эта диета кажется сложной, но полезной?

Here is a simple phonetic guide (not strict IPA, but close enough):

• Эта – [É-ta] (stress on Э)
• диета – [di-YÉ-ta] (stress on е: дие́та)
• кажется – [KÁ-zhi-tsa] (stress on ка; ж like measure, tsa like tsar without r)
• сложной – [SLOZH-noy] (stress on сло; жн together, like zh
  • n)
• но – [no] (short o, like in British not but shorter)
• полезной – [pa-LYEZ-noy] (stress on лез)

Main stress pattern:

Э́та диэ́та ка́жется сло́жной, но поле́зной.

What case and gender is диета, and how does that affect the adjectives?

Диета is:

• feminine gender
• singular
• nominative case (as the subject of the sentence)

Because of this:

1. The demonstrative pronoun must agree:

   • эта диета (feminine singular nominative)

2. The predicate adjectives must agree in gender and number with диета, and take instrumental case because of кажется:

   • feminine singular instrumental of сложный → сложной
   • feminine singular instrumental of полезный → полезной

So the whole agreement chain is:

• Эта (fem. nom.) диета (fem. nom.) кажется сложной (fem. instr.), но полезной (fem. instr.).