Philosophy

In all matters, Philosophy is the discipline of all rational dialogue required to properly separate things one does Know, from things they Do Not Know, and also from Opinion.

Know - Do Not Know - Opinion

A Philosopher, being a lover of wisdom, understands:

In all matters, it is wise to properly separate things you Know, from things one does you Do Not Know, and also from Opinion. It is the fool that mixes them.

The trichotomy of Know, Do Not Know, and Opinion is the foundation to all philosophical dialogue.

A Philosopher understands:

All objective terminologhy given to a certain system, is philoophical dialogue. In a different given certain system, the meaning of terminology may change.

For one to assert a thing they Do Not Know is a thing they Know, is irrational. It is not philosophical dialogue, it is arguing.

For one to assert a thing they Do Not Know is an Opinion, is irrational. It is not philosophical dialogue, it is arguing.

Things you Do Not Know are to be held as things to be questioned.

It is irrational to argue "No one can know any thing with absolute certainty.", as according to the dichotomy of certainty vs uncertainty, this would be in your list of things that remain uncertain, therefore it is you admitting to being uncertain if it is possible to know a thing for certain or not, therefore you are only asking "Is it possible to know a thing for certain or not?".

Philosophical skepticism is understanding there are things known for certain and there are things that remain uncertain, and understanding that with proof and reproof can a thing be known for certain.