Я знаю, что сладкая газировка вредная.

I know that sweet soda is harmful.

Breakdown of Я знаю, что сладкая газировка вредная.

• я: I
• сладкий: sweet
• что: that
• знать: to know
• газировка: the soda
• вредный: unhealthy

Questions & Answers about Я знаю, что сладкая газировка вредная.

Why is there a comma before что?

In Russian, a comma is normally placed before что when что introduces a subordinate clause (a dependent clause).

• Main clause: Я знаю – I know
• Subordinate clause: что сладкая газировка вредная – that sweet soda is unhealthy

Since что introduces the subordinate clause, you must write a comma:
Я знаю, что сладкая газировка вредная.

Can что be omitted like English that in “I know (that) sweet soda is unhealthy”?

Most of the time in Russian, что is not omitted in this kind of sentence. The natural, standard version is:

• Я знаю, что сладкая газировка вредная.

Leaving что out – Я знаю сладкая газировка вредная – sounds wrong or at least very unnatural.

In some other constructions or in very colloquial speech, что can sometimes be dropped, but after verbs like знать, думать, считать, it is usually kept.

Why is it сладкая газировка, not something like сладкое газировка?

Because adjectives in Russian agree with the noun they describe in:

• Gender
• Number
• Case

Газировка is:

• feminine
• singular
• nominative case (subject of the clause)

The adjective сладкий in the feminine, singular, nominative form is сладкая. So you must say:

• сладкая газировка – sweet soda

Сладкое is neuter singular nominative. It would agree with a neuter noun like молоко (milk): сладкое молоко. It does not agree with газировка, so you cannot use сладкое here.

How do I know that газировка is feminine?

A very common pattern in Russian:

• Nouns ending in -а / -я are usually feminine.

Газировка ends in -а, so it is treated as feminine. There are exceptions (e.g. папа, дядя, which are masculine), but газировка is a normal feminine noun:

• она – she/it (for газировка)
• сладкая газировка (feminine adjective form)

Why is it вредная, not вредно?

Both exist in Russian but they play different roles.

1. Вредная – long-form adjective, feminine singular nominative, agreeing with a noun:

   • Газировка вредная. – The soda is unhealthy. (literally: soda (is) unhealthy)

2. Вредно – predicative adverb-like form (often used impersonally):

   • Пить сладкую газировку вредно. – It is unhealthy to drink sweet soda.

In your sentence, вредная describes газировка directly, so it has to agree in gender and number:

• сладкая газировка вредная – sweet soda is unhealthy

If you changed the sentence structure, you could use вредно:

• Я знаю, что пить сладкую газировку вредно. – I know that drinking sweet soda is unhealthy.

Why is there no word for “is” between газировка and вредная?

In the present tense, Russian normally omits the verb быть (to be) when it acts as a simple link between subject and predicate.

So instead of:

• ✗ Газировка есть вредная.

You say:

• Газировка вредная. – literally: Soda unhealthy → Soda is unhealthy.

The same thing happens in your sentence:

• …что сладкая газировка вредная. – that sweet soda is unhealthy.

In the past or future you do use forms of быть:

• Газировка была вредной. – Soda was unhealthy.
• Газировка будет вредной. – Soda will be unhealthy.

Why is газировка in the nominative case and not accusative?

Inside the subordinate clause (что сладкая газировка вредная), газировка is the subject of that clause:

• (что) – that
• сладкая газировка – sweet soda (subject)
• вредная – is unhealthy (predicate adjective)

Subjects are in the nominative case, so газировка stays in nominative:

• газировка (nom.) – not газировку (acc.)

If газировка were a direct object, it would be accusative:

• Я пью газировку. – I drink soda. (Here газировку is accusative, direct object of пью.)

Could I change the word order and say Я знаю, что вредная сладкая газировка?

You can rearrange adjectives before the noun, but you still need a clear predicate. The pattern:

• [subject] [predicate adjective]

must be preserved. Some variants:

1. Normal, neutral word order:

   • Я знаю, что сладкая газировка вредная.

2. Slight emphasis on “unhealthy”: move it forward inside the clause but keep predicate function clear:

   • Я знаю, что вредная сладкая газировка.
     This is grammatically possible, but it sounds unusual and stylistically marked; listeners might expect something after it, or interpret it as incomplete.

However, if you separate clearly:

• Я знаю, что сладкая газировка вредна. (short form, see next Q)
• Я знаю, что вредна сладкая газировка.

Both of these are fine and put different emphasis on вредна vs сладкая газировка:

• Сладкая газировка вредна. – neutral
• Вредна сладкая газировка. – more emphasis on вредна (“It is unhealthy that sweet soda…” / “Unhealthy is sweet soda.”)

What is the difference between вредная and вредна in this sentence?

Both can work, but they are different forms:

• вредная – full (long) adjective, feminine, singular, nominative
• вредна – short-form adjective, feminine, singular

Possible variants:

• Я знаю, что сладкая газировка вредная.
• Я знаю, что сладкая газировка вредна.

Meaning: essentially the same – I know that sweet soda is unhealthy.

Nuances:

• Long form (вредная) is the default descriptive form, very neutral.
• Short form (вредна) often feels a bit more concise, can sound slightly more “bookish” or emphasize the quality as a fact or state.

Both are correct in standard Russian.

Why is it что, not чтобы?

Что and чтобы introduce different types of subordinate clauses.

• Что is used for factual content, like that something is the case:

  • Я знаю, что сладкая газировка вредная.
    I know that sweet soda is unhealthy.

• Чтобы is used for purpose, intention, or desired result, often with verbs of wanting, needing, asking, etc.:

  • Я хочу, чтобы ты не пил сладкую газировку.
    I want you not to drink sweet soda.
  • Он сделал это, чтобы помочь. – He did it in order to help.

In your sentence, you are just stating a fact you know, not a purpose or wish, so что is correct, not чтобы.

What is the aspect and tense of знаю, and why that form?

Знаю is:

• Present tense
• First person singular
• Imperfective aspect of the verb знать (to know)

In Russian, знать is normally used in the imperfective to express a state or permanent knowledge:

• Я знаю, что… – I know that… (a current state of knowing)

The perfective counterpart (узнать) means to find out, to come to know:

• Я узнал, что сладкая газировка вредная.
  I found out / I learned that sweet soda is unhealthy.

How is the sentence pronounced? Where is the stress in each word?

Word-by-word with stress marks (capital letters show the stressed syllable):

• Я – ya (only one syllable, stress on it)
• знаю – ЗНА-ю (ZNÁ-yu)
• что – shto (stress on the only syllable)
• сладкая – СЛА-дко-я (SLÁD-ka-ya, often phonetically SLÁT-ka-ya)
• газировка – га-зир-ОВ-ка (ga-zir-ÓF-ka, often with /f/ sound)
• вредная – ВРЕД-на-я (VRÉD-na-ya)

So the rhythm is:

Я ЗНА-ю, что СЛА-дка-я га-зир-ОВ-ка ВРЕД-на-я.

Could the whole sentence be said more briefly in Russian while keeping the same meaning?

Yes, there are shorter, more colloquial ways to express the same idea:

• Я знаю, что газировка вредная. – You drop сладкая if sweetness is understood from context.
• Знаю, что сладкая газировка вредная. – Drop я; subject is implied.
• Знаю, что газировка вредная.

But if you specifically want to say sweet soda, then your original sentence is perfectly natural and clear:

• Я знаю, что сладкая газировка вредная.