Here's why:
* It's a proper noun: "English" refers to a specific language, much like "Spanish" or "French." Proper nouns are always capitalized.
* It's a subject name: When we talk about specific academic subjects, we treat them as proper nouns. For example, we say "Math," "History," and "Science."
Examples:
* I took an English class last semester.
* My favorite subject is English.
* I need to study for my English exam.