4-Object is a directory for headings pertaining to objects.
Your car and your computer are objects. You are a person but your body is an object. The Earth is a place, not an object.
1-persint 2-by-Material 3-by-Type 4-by-Func 5-by-Department
Material - what it's made of. Paper and water are materials.
Type - What kind of thing it is. E.g. containers, food, electronics.
Func - What it's for. E.g. travel kit, cooking equipment.
Department - What department it would be sold under. If something defies categorization by other means, someone still has to sell it, and thus it has a label.
File by cascade. If it isn't one material, is it a type? If it isn't one type, has it a function? If it hasn't one function, has it a department?