Learn Hardcore Russian: Мы каждый день говорим одно и то же.

Here, одно doesn’t refer to a specific noun like book or idea; it just stands for an undefined “thing”. Because that “thing” is abstract and not specified, Russian uses the neuter form:

одно и то же ≈ “the same thing” (unspecified, abstract)

If you specified the noun, agreement would change, for example:

одни и те же слова – “the same words” (plural)
одна и та же история – “the same story” (feminine)
один и тот же человек – “the same person” (masculine)

What is же in то же, and how is it different from тоже?

Же is a particle that adds emphasis or identity, often roughly “the very / exactly the same” in English.

In this sentence:

то же = то + же
- то = “that (one / thing)”
- же = particle emphasizing identity → “that same (thing)”

So одно и то же ≈ “one and that same (thing)” → “one and the same”.

This is different from тоже (written as one word), which means “also / too”:

Я тоже говорю. – “I also speak / I speak too.”
Мы говорим одно и то же. – “We say the same thing.”

So here it must be то же (two words), not тоже.

Why is то же written separately and not тоже?

Because they are different words with different meanings:

то же (two words): “that same (thing)”
- то – “that” (pronoun)
- же – particle
тоже (one word): “also / too”

Compare:

Мы говорим одно и то же. – “We say the same thing.”
Мы тоже говорим. – “We also speak / We speak too.”

In your sentence, the meaning is “the same thing”, so only то же is correct.

What grammatical case is одно и то же in here?

It is in the accusative case because it is the direct object of the verb говорим (“we say”).

Мы – subject (nominative plural)
говорим – verb (1st person plural, present)
одно и то же – what we say → direct object → accusative singular neuter

For neuter inanimate nouns and pronouns, nominative and accusative look the same, so you don’t see a form change, but the function here is clearly accusative.

What case is каждый день in, and why doesn’t it use a preposition?

Каждый день is in the accusative case and functions as an adverbial phrase of time: “every day”.

In Russian, expressions of time are often formed with bare accusative (no preposition):

каждый день – every day
каждый год – every year
весь день – (for) the whole day
целую неделю – (for) a whole week

So:

Мы каждый день говорим одно и то же.
– “We say the same thing every day.”

You do not say в каждый день in this meaning. В каждый день is either unnatural or used in rare, very specific contexts (e.g. in poetic or highly formal language).

Why is the verb говорим used and not скажем?

Russian verb aspect is important here:

говорить – imperfective (“to speak / to be saying / to say in general”)
сказать – perfective (“to say once, to have said, to finish saying”)

The phrase каждый день shows a repeated, habitual action, not a one-time completed event. For repeated/habitual actions in the present (and in general statements), Russian uses the imperfective:

Мы каждый день говорим одно и то же.
– “We (habitually) say the same thing every day.”

If you used скажем, it would sound like:

Мы скажем одно и то же.
– “We will say the same thing (once, in the future).”

Completely different meaning.

Can the word order change? For example, is Каждый день мы говорим одно и то же also correct?

Yes, Russian word order is relatively flexible here. All of these are grammatically correct:

Мы каждый день говорим одно и то же.
Каждый день мы говорим одно и то же.
Мы говорим одно и то же каждый день.

They all mean “We say the same thing every day”. The differences are mainly in emphasis:

Каждый день мы говорим одно и то же.
Puts slightly more focus on каждый день (“every day, we say…”).
Мы говорим одно и то же каждый день.
Puts the small focus shift to каждый день at the end (common in speech to add it as an afterthought).

Neutral default would probably be the original: Мы каждый день говорим одно и то же.

Could the subject мы be dropped, like in Spanish or Italian?

In standard Russian, pronouns are usually not dropped in the present tense, even though the verb ending (-им in говорим) already shows person and number.

You can omit мы in very specific contexts:

when it’s completely obvious from earlier context who “we” is,
in headlines, notes, or very colloquial speech.

But the normal, neutral version is with the pronoun:

Мы каждый день говорим одно и то же. – natural, standard
Каждый день говорим одно и то же. – possible, but sounds more like a note, a slogan, or very informal speech, or like you are continuing a thought (“(We) say the same thing every day.”)

Why is there no explicit word for “thing” in Russian, like “the same thing”?

Russian often doesn’t need an explicit word like “thing” (вещь) where English does.

одно и то же by itself already means “the same thing”.
The idea of some “thing” is built into одно (one) and то (that).

If you try to add an explicit noun like вещь, it either changes the meaning or sounds unnatural:

Мы каждый день говорим одну и ту же вещь.
Grammatically possible, but sounds heavy, more like “we say the same remark / the same statement” – you’re stressing that it is a particular “thing” (utterance).

The idiomatic, natural way to say “We say the same thing every day” is exactly:

Мы каждый день говорим одно и то же.

Are there similar expressions to одно и то же I should know?

Yes, some very common related patterns:

тот же / та же / то же / те же – “the same (one)”
- тот же человек – the same person (masc.)
- та же проблема – the same problem (fem.)
- то же место – the same place (neut.)
- те же люди – the same people (pl.)
тот же самый / та же самая / то же самое / те же самые – stronger emphasis, “the very same (exact same)”
- тот же самый человек – the very same person
- то же самое – the same thing / exactly the same
Short standalone pronoun:
- то же самое – “the same (thing)”
  - Он сказал то же самое. – “He said the same (thing).”

Your phrase одно и то же is especially common in the context of repetition: “the same thing over and over again”.