Картонная коробка лежит на полу.

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Breakdown of Картонная коробка лежит на полу.

• лежать: to lie
• пол: the floor
• картонная коробка: the cardboard box

Questions & Answers about Картонная коробка лежит на полу.

Why is it картонная, not картонный?

Because картонная is an adjective modifying коробка, and Russian adjectives must agree with the noun in gender, number, and case.

Here, коробка is:

• feminine
• singular
• nominative

So the adjective also has to be feminine singular nominative: картонная.

Compare:

• картонная коробка = a cardboard box
• картонный ящик = a cardboard crate/box, with ящик being masculine

Why is it коробка, not коробку or some other form?

Коробка is in the nominative case because it is the subject of the sentence — the thing that is doing the action of лежит.

In English, we do not usually see this change clearly, but in Russian the subject normally appears in the nominative.

Compare:

• Коробка лежит на полу. = the box is lying on the floor
• Я вижу коробку. = I see the box

In the second sentence, коробку is a direct object, so it changes case.

What exactly is лежит?