りかい します Or わかります


I want to say "Brother will understand it," so should I use:

> あに は それ を りかい します。

Or

> あに は それ を わかります。

What other parameters am I missing?  
Is the first one preferred more and if so, why?




Is this something that brother would understand, but probably not another
person? If so, I would use this expression:

> [兄]{あに}なら[分]{わ}かると[思]{おも}います。

The particle ”を” is not commonly used with the verb 分かる (though it is in rare
cases), "が" is usually more appropriate. However, it is best to omit "それが"
since it is implied.

Also, without the "と思います" part (or "と思う"), it feels very definitive to me,
like you are 100% sure. I think it's safer to add the "I think" part.

Finally, "[理解]{りかい}する" is a verb that isn't used that often in daily
conversation, though it means something similar to わかる. I have heard it most
used in the expression "理解できない！" which is when someone is complaining "I can't
even comprehend what so-and-so is doing", though there are other uses as well.

