Learn Croatian: Vidiš li pametnog dječaka?

The boy is the direct object of the verb vidiš (to see), so we use the accusative case. Because a boy is a living being (animate), masculine nouns add an -a to become dječaka. The adjective must match this, so pametan takes the animate masculine ending -og, becoming pametnog.

Where did the a from the dictionary form pametan go?

The word pametan has what is called a 'fleeting a'. This is an a near the end of a base word that disappears when you add grammatical endings. When we add the -og ending, the a drops out, giving us pametnog instead of pametanog.

What does the word li do here?

The word li is a question particle used to ask yes/no questions. It does not have a direct translation in English, but it changes a statement into a question. It usually takes the second spot in a sentence, right after the first word (vidiš).

Where is the word for 'you' in this sentence?

In Croatian, the pronoun ti (you) is usually left out because the verb ending already shows who is acting. The -š at the end of vidiš tells us it means 'you see'. Including ti isn't necessary unless you want to specifically emphasize who is looking.