<|im_start|>system
You are a helpful AI assistant.<|im_end|>
<|im_start|>user
When is a door not a door?<|im_end|>
<|im_start|>assistant
A door is not a door when it is ajar, or open. When a door is open, it is no longer fulfilling its function as a barrier, and is instead allowing access through an opening.<|im_end|>
<|im_start|>user
how can a door be a jar?<|im_end|>
<|im_start|>assistant
If you are asking me how a door can be "ajar" then a door is "ajar" when it is slightly open, leaving an air gap. 

Here are some examples:
The door was ajar.
My email is open and Twitter ajar for your musings.
Turn off the oven and put the cheesecake back in with the door ajar.
The lid had come slightly ajar; the bird was straining at the gap.<|im_end|>
<|im_start|>user
What properties can door have that make a door not a door?<|im_end|>
<|im_start|>assistant
A door is considered not a door when it does not fulfill the basic function and purpose of a door, which is to provide an opening or a barrier between two spaces. Some properties that could make a door not a door include:

Lack of a hinge mechanism to swing open or close
Inability to lock or secure the opening
Lack of appropriate size or shape to effectively block the opening
Absence of a handle or knob to open and close the door
Material that is not suitable for a door, such as a sheer curtain or a piece of cloth
In essence, if a structure or object fails to provide the basic functions of a door, it would not be considered a door.<|im_end|>