We should use essential attributes in classifying things.
An essential attribute is a fundamental one. If we divide a
genus according to an essential attribute, we group
together things that are fundamentally similar and separate
them from things that are fundamentally different.
Because a fundamental attribute underlies and explains many of a
thing's superficial attributes, things that are fundamentally
similar probably have many attributes in common; things that
share a superficial, nonessential attribute may well have
nothing else in common.
If we classify animals by color, then animals that have more
differences than similarities, such as elephants and mosquitoes,
are grouped together, whereas animals that have more
similarities than differences, such as cardinals and canaries,
are distinguished from each other and placed in different