Learn Hardcore Turkish: Yorgan yumuşak ve sıcak.

In simple present descriptions, Turkish omits the copula “to be”. Instead of saying “Yorgan yumuşak ve sıcak dir”, you drop “dir” in everyday speech.

Why do the adjectives yumuşak and sıcak come after yorgan, whereas in English they precede the noun?

Here they’re used predicatively (they describe the subject). Predicative adjectives follow the noun in Turkish. If you want to use them attributively (directly before the noun), you’d say yumuşak ve sıcak yorgan (“a soft and warm duvet”).

Why aren’t yumuşak and sıcak inflected for number, gender, or case? Shouldn’t they agree with yorgan?

Turkish adjectives never change form for number, gender, or case. They stay the same whether they describe one or many items, or appear in different grammatical cases.

Why isn’t yorgan marked with any case ending?

The nominative case (used for the subject in a non-transitive clause) is unmarked in Turkish. So yorgan stays in its bare form.

Why isn’t there any article like “the” or “a” before yorgan?

Turkish has no definite or indefinite articles. A bare noun like yorgan can mean “a duvet” or “the duvet” depending on context.

How would you negate this sentence? How do you say “The duvet is not soft and warm”?

Place değil after the adjectives:
Yorgan yumuşak ve sıcak değil.

How can I ask “Is the duvet soft and warm?” in Turkish?

You have two options:
1) Rely on intonation: Yorgan yumuşak ve sıcak?
2) Add the question particle mi after the last adjective: Yorgan yumuşak ve sıcak mı?

What if I want to say “Duvets are soft and warm”? How do I pluralize?

Make the noun plural with -lar (or -ler after front vowels) but leave adjectives unchanged:
Yorganlar yumuşak ve sıcak.