知道
zhīdào
Why "知道了" works as a reply, not a statement
The picture A loose fact slides in from outside and comes to rest in a drawer in your head. 知道 is the fact resting in the drawer; 认识 is having stood face to face with the person.
Where the picture shows up in 知道
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already in the drawer
我知道你的名字。
wǒ zhīdào nǐ de míngzi
I know your name.
The drawer slides open and the slip with the name is already lying there
-
it just landed
知道了，我马上过去。
zhīdào le, wǒ mǎshàng guòqù
Got it — I'll be right over.
The words drop through the ear and land in the drawer with a small thud
-
the drawer is empty
我不知道怎么用这个机器。
wǒ bù zhīdào zěnme yòng zhège jīqì
I don't know how to use this machine.
Standing at the machine, pulling the drawer open onto bare wood
-
it hasn't gone in yet
这件事老板还不知道。
zhè jiàn shì lǎobǎn hái bù zhīdào
The boss doesn't know about this yet.
The news waits outside the boss's office door, still not through it
-
knocking on someone's drawer
你知道他在哪儿吗？
nǐ zhīdào tā zài nǎr ma
Do you know where he is?
A finger taps someone else's drawer to see whether anything is inside
All of it in one picture
知道 is one picture: a piece of information parked in a drawer. The name is already in there, so you know it; something just landed in there, so "got it" is the whole reply. Pull the drawer open and find nothing, and that is not knowing; the news stalled outside the boss's door, and the boss still doesn't know. Tapping on someone else's drawer to see what's inside is how you ask.