Learn Hardcore Japanese: kono tokei ha hurui desu ga, mada ugokimasu.

この is a demonstrative adjective meaning this. It must come directly before a noun to indicate something near the speaker. In our sentence, この時計 means this clock (the one we’re talking about).

Why is the particle は placed after この時計 instead of が?

は marks the topic of the sentence—the thing we’re talking about. By saying この時計は, you set this clock as the subject of your comment. If you used が, it would mark the clock as an unidentified subject rather than the topic.

Why do we say 古いです instead of just 古い?

古い is an い-adjective meaning old. In polite speech, predicates (whether adjective or noun) take です to soften the statement. So 古いです = is old in a polite register. In casual speech you could drop です and just say 古い.

What role does が play in 古いですが?

Here, が is a conjunction meaning but or however. It connects the first clause (it is old) with the second clause (it still works). In polite speech が is common; more formal alternatives include けれども, and more casual you’d use けど.

Why is there no particle before 動きます? Wouldn’t you need が or を?

動く (“to move”/“to run [a machine]”) is an intransitive verb, so it doesn’t take a direct object or an object marker (を). And because この時計 is already the topic (marked by は), you don’t need to mark it again as the subject in the second clause.

What does まだ mean here, and why is it placed before 動きます?

まだ means still (affirmative) or yet (negative). In an affirmative sentence, まだ goes right before the verb to say it still does X. So まだ動きます means it still works/moves.

Could you show a more casual version of this sentence?

Certainly! In casual speech you might say:

この時計は古いけど、まだ動く。
Here, けど replaces the polite が, and both です and the ます ending are dropped in favor of the plain form 動く.

What’s the difference between まだ動きます and まだ動いています?

まだ動きます focuses on the capability or habitual action: it still works when you use it.
まだ動いています emphasizes the ongoing state at this moment: it is still moving (right now you can see it moving).

Why is there a comma after 古いですが? Is it necessary?

The comma indicates a slight pause and visually separates the two connected clauses. In Japanese writing, it’s common to put a comma before or after が when it acts as a conjunction. It isn’t grammatically mandatory, but it helps readability.