２つの節を however（しかしながら）や moreove（さらに）などの接続副詞でつなぐ場合に、セミコロンを用いることがあります。本来はピリオドを付けて別々の文にするものなので、カンマで代用することはできません。
○ You said that the design would be finished on January 3; however, it is already March 1.
○ You said that the design would be finished on January 3. However, it is already March 1.
× You said that the design would be finished on January 3, however, it is already March 1.
