Learn Hardcore German: Ich sehe meinen Zahn im Spiegel.

Because Zahn is masculine and here it’s the direct object of sehen, so you need the accusative case. In German, masculine nouns add -en to their articles and possessive pronouns in the accusative (der → den, mein → meinen).

What case is meinen Zahn, and how can I recognize it?

It’s the accusative case, marking the direct object (“what is being seen”). You spot it because the verb sehen requires a direct object, and masculine singular words in the accusative add -en to their article or possessive pronoun.

Why is the location im Spiegel instead of in den Spiegel?

Here in indicates static location (answering “where?”), which takes the dative case. Spiegel is masculine, so the dative article is dem, and in dem contracts to im. If you used in den Spiegel, that would be accusative, implying movement “into the mirror.”

How do I know the gender of Zahn and Spiegel, and why is it important?

Both Zahn and Spiegel are masculine (der Zahn, der Spiegel). You learn gender by memorizing each noun with its article. Gender is crucial because it determines case endings on articles, pronouns, and adjectives.

Why isn’t there a reflexive pronoun like mich in this sentence? Could I say Ich sehe mich im Spiegel?

You can say Ich sehe mich im Spiegel if you mean “I see myself in the mirror.” But in Ich sehe meinen Zahn im Spiegel, you’re specifying a part of yourself, not using a reflexive construction. sehen itself isn’t reflexive here.

Could I use anschauen or betrachten instead of sehen, and what’s the difference?

Yes. anschauen (“to look at”) and betrachten (“to observe”) both work but add nuance. Ich schaue meinen Zahn im Spiegel an emphasizes the act of looking closely; Ich betrachte meinen Zahn im Spiegel sounds more formal or scientific. sehen is more general.

What is the word order in Ich sehe meinen Zahn im Spiegel, and why?

German main clauses follow the Verb‑second rule: Subject (Ich) – Verb (sehe) – Object (meinen Zahn) – Adverbial phrase (im Spiegel). Adverbials of place come after objects unless you want to emphasize them.

Why not auf dem Spiegel or über dem Spiegel?

auf means “on,” and über means “above/over.” You’re not on top of or above the mirror; you’re looking in it. So you need in plus dative to express “inside” or “within” the mirror’s reflective surface.