Questions & Answers about Er isst einen Apfel und sieht den Film.
Why is the verb isst instead of esst?
The dictionary form of the verb is essen (to eat). Because it is a strong verb, its main vowel changes from e to i when used with er (he), sie (she), or es (it). That makes it er isst. The form esst does exist, but it is used for the you all form, which does not get a vowel change.
Why does sieht change to ie while isst only changes to i?
Strong verbs with an e in the stem can change to either i or ie for the du (you) and er/sie/es forms. It just depends on the verb. For essen, the e becomes an i (er isst). For sehen (to see), the e becomes an ie (er sieht). You simply have to memorize which pattern to use when you learn a new strong verb!
Why do we say einen Apfel and den Film instead of ein and der?
Both Apfel and Film are masculine nouns. In this sentence, they are the direct objects because they are receiving the actions (they are being eaten and watched). That puts them in the accusative case. In the accusative case, the masculine word for a/an changes from ein to einen, and the word for the changes from der to den.