Formality of "悲哀" as opposed to "悲傷" and "哀傷" From what I have learned, or I remember I have learned, 悲哀, 悲傷, and 哀傷 all mean sadness and are interchangeable. However, as I remember, I have read 悲傷 and 哀傷 in academic/professional writings, but not the word 悲哀. On the other hand, I have barely seen 悲傷 or 哀傷 used in colloquial context, such as on social networking sites. 

Is it the case that 悲哀 is preferred in colloquial context; while 悲傷 and 哀傷 are preferred in formal context? Or, if I was wrong, do they actually have different meanings?

Thanks in advance!
“哀伤” is usually a noun, while “悲伤” and “悲哀” are usually adjective.
“哀伤”, “悲伤” both could mean severe sadness, and are often used in the context that one has lost someone he loved or something he valued.

任何语言都无法形容他失去亲人的哀伤。
No words could describe the sorrow of losing his family.
刚刚失去亲人的他看起来十分悲伤。
Having lost his family, he looks very sad.

Though “悲哀” could mean sadness in some context (like on a funeral), it mostly means “pitiful”, and is more often used to describe things rather than emotion.

人，失去了梦想，是多么悲哀的事情。
How pitiful it is, when one loses his dreams.
你为了金钱丧失了尊严，我真为你感到悲哀！
You lost your honor for money. I feel sorry for you.