Kana pronunciation is not completely unambiguous. は and へ have different pronunciation when they're being used as particles. Additionally, there is pitch accent

Kana pronunciation is not completely unambiguous. は and へ have different pronunciation when they're being used as particles. Additionally, there is pitch accent, where small differences in pitch can change meaning. (Although pitch accent varies between regional dialects and you can almost always guess the meaning from context so it's not critical for understanding.)