理解 and 了解: Understanding and acknowledging information
Compare understanding a mechanism or cultural difference with acknowledging a change and understanding circumstances before taking charge. Read the overlap in meaning and the actions actually stated in each example.
Understanding a mechanism or cultural difference
理解 includes understanding. The mechanism and cultural-difference examples identify the content to be understood and relate that understanding to a diagram or careful listening.
「図解を読むと、機械が動く仕組みを理解しやすくなります。」 (A diagram makes it easier to understand how the machine works.) Reading the diagram makes the mechanism easier to understand. Help with understanding does not establish that all of the mechanism has already been understood.
Acknowledging a change and understanding circumstances
了解 includes understanding or acknowledgment. It can acknowledge a change of meeting place and can also refer to understanding circumstances; it is not restricted to an empty reply.
「事情を了解した上で、担当を引き受けた。」 (After understanding the circumstances, I took charge.) This sentence reports taking charge after understanding the circumstances. It does not form a sequence with the separate example about a changed meeting place.
A reply and a later action must be read separately
「集合場所の変更、了解しました。」 (I understand that the meeting place has changed.) The response acknowledges the change of meeting place. It does not report arrival there or performance of the task mentioned in the other example.
Despite the overlap in understanding, distinguish each sentence's content, response, and action. Do not exclude responses from 理解 or content understanding from 了解, or add unsupported rules about a speaker's rank or a fixed politeness order.
What is confirmed in 集合場所の変更、了解しました and the example of understanding the circumstances with 了解 before taking charge?
Show the answer and why
The first acknowledges the changed meeting place without reporting arrival. The second reports understanding the circumstances and then taking charge. They are separate examples, and 了解 is not restricted to a reply without content understanding.