In order to extrapolate objectively valid principles from our experience, it is imperative that we not introduce any arbitrary notions. An arbitrary notion is one that is not connected to one's experience of reality—that is, a notion not supported by evidence (or logic based on evidence). It may be wondered, however, whether arbitrary notions should at least be entertained as "possibilities." The logical consequences of accepting such arbitrary "possibilities" are indicated by the following dialogue.

Dialogue 1: An individual whom we shall call AGNOSTIC, who is perhaps overanxious not to appear narrow-minded, is drawn into the following discussion with a person we shall call MYSTIC A.

MYSTIC A: You claim to know certain things, either by experience or by deductions based on that experience, do you not?

AGNOSTIC: Certainly. I know that 1 + 1 = 2 and that Socrates was a mortal.

MYSTIC A: Well, how do you know that some alien has not implanted a device in your brain? How do you know that he is not manipulating your thoughts at this moment, making you think those things even though they are false?

Dialogue 1: An individual whom we shall call AGNOSTIC, who is perhaps overanxious not to appear narrow-minded, is drawn into the following discussion with a person we shall call MYSTIC A.
MYSTIC A:	You claim to know certain things, either by experience or by deductions based on that experience, do you not?
AGNOSTIC:	Certainly. I know that 1 + 1 = 2 and that Socrates was a mortal.
MYSTIC A:	Well, how do you know that some alien has not implanted a device in your brain? How do you know that he is not manipulating your thoughts at this moment, making you think those things even though they are false?