“Consider that everything is opinion, and opinion is in thy power.”

"Reality"
The Doubter's Companion (1994)

Source: Means and Ends of Education (1895), Chapter 1 "Truth and Love"

Source: Political Aphorisms, Moral and Philosophical Thoughts (1848), p. 248

22
Sovereign Maxims

Misattributed
Source: Cited as being from The Meditations. This quote does not exist there; although there are several other statements about everything being an opinion, none of these are connected to a sentence about perspectives.

Preface, § 2
The Phenomenology of Spirit (1807)

As quoted in The Life and Writings of Thomas Jefferson : Including All of His Important Utterances on Public Questions (1900) by Samuel E. Forman, p. 429
Posthumous publications

Source: Demian (1919), p. 167
Context: We ought not to consider the opinions of those sects as naïve as they appear from the rationalist point of view. Science as we know it today was unknown to antiquity. Instead there existed a preoccupation with philosophical and mystical truths which was highly developed. What grew out of this preoccupation was to some extent merely pedestrian magic and frivolity; perhaps it frequently led to deceptions and crimes, but this magic, too, had noble antecedents in a profound philosophy. As, for instance, the teachings concerning Abraxas which I cited a moment ago. This name occurs in connection with Greek magical formulas and is frequently considered to be the name of some magician's helper such as certain uncivilized tribes believe in even at present. But it appears that Abraxas has much deeper significance. We may conceive of the name as that of the godhead whose symbolic task is the uniting of godly and devilish elements.