English, like all languages, has changed over the years. In modern English, you only have to choose between “you” and “your” to talk about the person you’re speaking to. But English used to have different words for “you” depending on how the word fit into the sentence (just like Spanish and other languages). If it was the subject, it was “thou”: “Thou art beautiful.” If it was the object, it was “thee”: “I will send thee a letter.”
全ての言語と同じく、英語も長年にわたり変化しています。現代英語は話し相手のことを言うとき「you」と「your」のどちらかを選ぶだけです。しかし昔は（スペイン語などと同じように）、文章によって様々な「you」がありました。主語なら「thou」。「あなたは美しい」。目的語なら「thee」。「あなたに手紙を送る」。
