Reply quickly.If the occasion is small then you can reply by telephone,but if tit is a big occasion it is better tot reply by letter.It is kinder to do this because it helps your host to remember and to organize things. If the invitation was by formal invitation them you might like to reply in formal way.Reply quickly. If the occasion is small then you can reply by telephone, but if tit is a big occasion it is better tot reply by letter. It is kinder to do this because it helps your host to remember and to organize things. If the invitation was by formal invitation them you might like to reply in formal way