Learn Hardcore Czech: Mám nové tričko, které je červené a velmi pohodlné. - I have a new T-shirt which is red and very comfortable.

Mám already clearly means I have (1st person singular).
Já mám is also correct, but it sounds more emphatic, like I (as opposed to someone else) have a new T‑shirt.

So the neutral, natural version is simply Mám nové tričko… without já.

Why is it nové tričko and not nový tričko?

Because tričko is a neuter noun, and adjectives must agree with nouns in gender, number, and case.

Dictionary form of the adjective: nový (masculine).
Neuter singular (nominative and accusative): nové.

So:

nový – masculine (e.g. nový telefon – new phone)
nová – feminine (e.g. nová kniha – new book)
nové – neuter (e.g. nové tričko – new T‑shirt)

Since tričko is neuter, we need nové.

Why is tričko in this form? Is it nominative or accusative?

Grammatically, tričko here is in the accusative singular, because it is the direct object of the verb mám (to have).

The verb mít (to have) takes a direct object in the accusative.
For neuter nouns, nominative singular and accusative singular look the same.

So even though tričko looks like nominative, its function in the sentence is accusative:

(Já) mám co? – nové tričko.
→ tričko is the thing you have = direct object = accusative.

What does které mean here, and why not který or která?

Které is a relative pronoun meaning which / that. It refers back to tričko.

Relative pronouns must agree in gender and number with the noun they refer to:

který – masculine (e.g. muž, který… – the man who…)
která – feminine (e.g. žena, která… – the woman who…)
které – neuter (e.g. tričko, které… – the T‑shirt which…)

Since tričko is neuter singular, the correct form is které.

In this sentence, které is also in the nominative, because it is the subject of the clause které je červené a velmi pohodlné (the T‑shirt which is red and very comfortable).

Why do červené and pohodlné both end in -é?

Both adjectives červené (red) and pohodlné (comfortable) describe tričko, which is:

neuter
singular
in the nominative (it’s the subject in the clause: které je…)

Adjectives must agree with the noun they describe:

neuter singular nominative → -é ending

So we get:

červené tričko – a red T‑shirt
pohodlné tričko – a comfortable T‑shirt
tričko, které je červené a velmi pohodlné – a T‑shirt which is red and very comfortable

Both adjectives share the same pattern because both refer to tričko.

Why do we need je? In English we sometimes drop “that is”, so can we drop je?

In English, you can say:

I have a new T‑shirt, red and very comfortable. (no that is)

In Czech, you cannot simply drop je in this kind of relative clause. You must keep the verb být (to be):

Mám nové tričko, které je červené a velmi pohodlné. ✅
Mám nové tričko, které červené a velmi pohodlné. ❌ (wrong)

You can drop které je in a different construction, but then the structure changes (see the next question).

Can I say Mám nové červené a velmi pohodlné tričko instead?

Yes, that is perfectly correct, just a different structure:

Mám nové tričko, které je červené a velmi pohodlné.
→ literally: I have a new T‑shirt which is red and very comfortable. (with a relative clause)
Mám nové červené a velmi pohodlné tričko.
→ literally: I have a new, red and very comfortable T‑shirt. (all adjectives are directly in front of the noun)

Both are natural. The second one is a bit more compact, with a simple string of adjectives modifying tričko.

Is the comma before které always necessary?

Yes, in this sentence the comma before které is required.

In Czech, you generally put a comma before a relative clause introduced by který / která / které when it adds extra information about a specific noun, similar to non‑restrictive relative clauses in English:

Mám nové tričko, které je červené a velmi pohodlné.

You’re talking about a specific T‑shirt that you already mentioned as “new”, and then adding a description. So the comma is needed.

Could I use co instead of které, like tričko, co je červené…?

Colloquially, people do say things like:

Mám nové tričko, co je červené a velmi pohodlné.

However:

který / která / které is more standard and correct in written Czech and in careful speech.
co in this role is more informal / colloquial.

For learning and for formal or neutral style, it’s better to use které here.

What is the difference between velmi pohodlné and something like moc pohodlné?

Both mean very comfortable, but with a slight stylistic difference:

velmi pohodlné
– neutral, a bit more formal / standard
– good in writing, in careful speech
moc pohodlné, hodně pohodlné
– more colloquial / everyday
– common in spoken Czech

All are understandable. In this sentence, velmi pohodlné sounds nicely neutral and standard.

How would I say the whole sentence without a relative clause, using just adjectives?

You can move the information from the relative clause into a series of adjectives before the noun:

Mám nové červené a velmi pohodlné tričko.

Here, nové, červené, and pohodlné are all just adjectives modifying tričko directly, instead of using které je….

What exactly does tričko mean? Is it the same as “shirt”?

Tričko is specifically a T‑shirt (usually short‑sleeved, casual, knit fabric).

tričko – T‑shirt
košile – shirt (typically with a collar and buttons, like a dress shirt)
halenka – blouse (usually women’s top)

So Mám nové tričko… is more precisely I have a new T‑shirt…, not just a new shirt in general.

How do you pronounce the sound ř in červené?

The Czech sound ř (in červené) is unique and can be tricky for English speakers.

Very roughly:

Start with a rolled or trilled r.
At the same time, add a zh sound (like the s in measure).
It’s produced with the tongue vibrating against the ridge behind your upper teeth, with voicing.

There isn’t a perfect equivalent in English. Common advice for learners:

Practice r and ž separately.
Then try blending them into one fast sound: r
- ž → ř.
Listen to native recordings and imitate (for example, words like tři, řeka, dobře, červené).

Understanding that ř is its own sound (not just “r” or “zh”) is already a good start.