～にしては vs. ～としては

Question

I know one implies the thing I'm comparing actually is the thing I'm comparing it to, and the other doesn't.

Can someone suggest an easy example or trick for remembering which is which?

Answer 1

Just adding to an existing answer because I typically don't think of these two as comparisons, I look at it from a different angle than the OP.

I typically think of this as more of expectation rather than comparison for ～にしては, although comparison could be valid as well but I never think of it like that.

So as @istrasci pointed out, ～にしては means "Considering X is Y...". There is an expectation involved because it typically goes against what the speaker is expecting from X.

From @istrasci's example, we have

トムはお金持ちにしては、あまりぜいたくな人生をおくらない(Considering Tom is pretty rich, he doesn't lead a very luxurious lifestyle)

Normally we usually expect rich people to lead a luxurious life, but in this case, Tom does not lead a luxurious life, therefore it goes against an expectation. So it is used to contrast a reality (does not live a luxurious life style) to some kind of expectation (rich people typically live in luxurious life style)

Another example:

スキーは初めてだと聞いていたが、それにしては、なかなかうまく滑るじゃないか。(I heard this is (your) first time skiing, considering this is (your) first time, you were pretty good)

This is another example of contrast between reality (you were a first time skier and you were pretty good), to an expectation (first time skiers are not good)

For me ～として implies and empathize some kind of position.

弁護士であるわたしとしては、それを勧めるわけにはいかない (As a lawyer, I cannot recommend (doing) that)

Lawyer is a position being empathized here.

学生として参加する (Apply/join as a student)

Student is a position being empathized here, I don't just want to apply, I want empathize that I want to apply as a Student.

Answer 2

～にしては means "Considering X is Y, ..."

トムはお金持ちにしては、あまりぜいたくな人生をおくらない (Considering Tom is pretty rich, he doesn't lead a very luxurious lifestyle

～としては mean "As a / In the capacity of X, ..."

弁護士であるわたしとしては、それを勧めるわけにはいかない (As a lawyer, I cannot recommend (doing) that)

So the latter is when the thing actually is the thing you're comparing to.