from :

http://blog.cybertranslator.idv.tw/?tag=%E5%B0%8F%E5%AF%AB

1.如果當下針對當事人,稱謂需大寫,或於家族成員間提及當事人則也需大寫.

a. Please pass the pepper for me, Dad.

b. Be polite , Son!

c. Did Dad tell you he will be right back, Sis?

d. Mom, Uncle Sam's phone!

2. 提及的當事人不在場則小寫

a. I wrote an e-amil to my dad.

b. I met my student's mom.