Breakdown of Тебе нельзя покупать этот острый перец!
ты
you (singular)
этот
this [f: эта, n: это]
покупать
to buy
нельзя
one must not
Questions & Answers about Тебе нельзя покупать этот острый перец!
Why does the sentence start with the Dative pronoun Тебе instead of Ты?
The word нельзя (must not / forbidden) is an impersonal word. In Russian, the person who is not allowed to do something is considered the receiver of the rule, so they take the Dative case. That is why we use тебе instead of the basic Nominative ты.
Why do we use the imperfective verb покупать here instead of the perfective купить?
When нельзя means "must not" or expresses a strict prohibition, it must be followed by an imperfective verb like покупать. If you used the perfective verb (нельзя купить), it would completely change the meaning to "it is impossible to buy" (for instance, because the store is sold out).
Since our lesson is about comparatives, how would I change острый to say "This pepper is spicier"?
To make the comparative form of острый (spicy), you drop the adjective ending and add -ее or -ей. To say "This pepper is spicier", you would say Этот перец острее. If you wanted to say "Buy a spicier pepper", you would use the compound form более острый перец because the short comparative острее cannot be placed directly before a noun.
Why does этот острый перец look like it is in the Nominative case if it is the object being bought?