Learn Hardcore Polish: On choruje rzadko, ale dziś naprawdę czuje się chory. - He is ill rarely, but today he really feels sick.

Choruje rzadko – grammatically fine, and very natural in context when it’s clear who you’re talking about.
On choruje rzadko – adds a bit of emphasis on “he”, for example:
- contrasting with someone else: On choruje rzadko, ale jego siostra często choruje.
  (He rarely gets sick, but his sister often does.)

So on is not grammatically required; it’s used for clarity or emphasis.

What is the difference between choruje and jest chory?

Both are related to being ill, but they’re used differently:

choruje – from chorować, a verb meaning to be ill / to suffer from an illness / to fall ill.
- In the present tense, it often expresses a habitual or repeated action:
  - On choruje rzadko. – He rarely gets ill / He rarely falls ill.
jest chory – literally “is ill”, describing a current state.
- On jest chory. – He is ill (now).

In the sentence:

On choruje rzadko – describes his general pattern: he rarely gets sick.
ale dziś naprawdę czuje się chory – today he feels ill (current state).

You could say On rzadko jest chory, but On choruje rzadko sounds more natural for “he rarely gets ill” as a general tendency.

Why is the adverb rzadko placed after choruje? Can I say On rzadko choruje?

Both word orders are correct:

On choruje rzadko.
On rzadko choruje.

Differences are subtle:

On rzadko choruje – is probably the most common, neutral word order.
On choruje rzadko – slightly emphasizes the rzadko at the end, as if stressing “and that’s rare”.

In everyday speech, On rzadko choruje is very typical, but your original sentence is also fully natural.

Why is there a comma before ale?

In Polish, you normally put a comma before the conjunction ale (but) when it connects two clauses:

On choruje rzadko, ale dziś naprawdę czuje się chory.

Each part could stand as a sentence:

On choruje rzadko.
Dziś naprawdę czuje się chory.

Because they are joined by ale, Polish spelling rules require a comma before ale.

What is the difference between dziś and dzisiaj?

dziś and dzisiaj both mean today and are almost completely interchangeable:

dziś – slightly shorter, often feels a bit more colloquial or compact, but very common in both speech and writing.
dzisiaj – a bit longer, also fully standard and common.

In your sentence, you can say:

… ale dziś naprawdę czuje się chory.
… ale dzisiaj naprawdę czuje się chory.

No change in meaning.

What does naprawdę add here, and where can it go in the sentence?

naprawdę means really / truly / actually. It emphasises the reality or seriousness of the statement:

dziś naprawdę czuje się chory – today he really feels ill (not just a little, and not pretending).

Other natural placements:

… ale naprawdę dziś czuje się chory.
… ale dziś czuje się naprawdę chory.

All are possible, but the most neutral is probably:

… ale dziś naprawdę czuje się chory.

Word order with adverbs is fairly flexible in Polish; moving naprawdę changes nuance or emphasis more than grammaticality.

Why do we say czuje się chory and not just czuje chory?

The verb czuć się means to feel (a certain way), and it requires the reflexive pronoun się:

czuć – to feel (something):
- Czuję ból. – I feel pain.
czuć się – to feel (a certain state):
- Czuję się chory. – I feel ill.
- Czuję się szczęśliwy. – I feel happy.

So czuje chory is incorrect. You must say czuje się chory (or źle się czuje, etc.) when talking about how someone feels.

What is the difference between czuje się chory and jest chory?

Subtle but useful difference:

jest chory – is ill (objective state, a bit more factual).
czuje się chory – feels ill (how he subjectively experiences it).

Examples:

On jest chory, ma wysoką gorączkę. – He is ill, he has a high fever.
On dziś czuje się chory, chociaż lekarz nic nie znalazł. – Today he feels ill, although the doctor didn’t find anything.

In your sentence, czuje się chory focuses on how he feels today, contrasting with his usual pattern (choruje rzadko).

Why is chory in the masculine form, and how would it change for a woman?

chory is an adjective meaning ill / sick. In Polish, adjectives must agree with the noun (or pronoun) in gender, number and case.

Subject: On (he) → masculine singular → chory

For a woman, you would change it to the feminine form:

Ona choruje rzadko, ale dziś naprawdę czuje się chora.

Other forms (for reference):

masculine: chory
feminine: chora
neuter: chore
plural (mixed or all-male group): chorzy
plural (all-female group): chore

Does choruje here mean “he is sick now” or “he tends to get sick”? How does Polish present tense work here?

In Polish, the present tense of imperfective verbs like chorować can express:

An action happening right now, or
A habit / general truth.

Here, context and the adverb rzadko (rarely) make it clearly habitual:

On choruje rzadko – He rarely gets sick / He rarely falls ill. (general tendency)

If you wanted to stress the present, you’d usually add something like teraz (now):

On teraz choruje. – He is sick now.

But in your sentence, choruje rzadko means a general pattern, not the present moment.

Is the whole sentence in the present tense in English too? How would you translate it naturally?

Yes, both Polish clauses are in the present tense, but with different time adverbs:

On choruje rzadko – general present (habit).
ale dziś naprawdę czuje się chory – present situation, specified by dziś (today).

A natural English translation:

He rarely gets ill, but today he really feels sick.
or
He doesn’t get sick often, but today he really feels ill.

Both preserve the contrast between his usual pattern and his current condition.

Can I say Dziś naprawdę źle się czuje instead of dziś naprawdę czuje się chory? Is there a difference?

Yes, you can say:

Dziś naprawdę źle się czuje.

Both are correct but slightly different:

czuje się chory – he feels ill / sick (specifically about being ill).
źle się czuje – he feels bad / unwell (broader: tired, weak, in pain, etc., not necessarily clearly “ill”).

So:

… ale dziś naprawdę czuje się chory. – emphasizes that he feels sick today.
… ale dziś naprawdę źle się czuje. – emphasizes that he feels bad / unwell today, maybe not formally “ill”.