The terms good and bad indicate no positive quality in things regarded in themselves, but are merely modes of thinking or notions, which we form from the comparison of things one with another. Thus one and the same thing can be at the same time good, bad, and indifferent. For instance, music is good for him that is melancholy, bad for him that mourns; for him that is deaf; it is neither good nor bad.
Baruch SpinozaIf we conceive that anyone loves, desires, or hates anything which we ourselves love, desire, or hate, we shall thereupon regard the thing in question with more steadfast love, etc. On the contrary, if we think that anyone shrinks from something that we love, we shall undergo vacillation of the soul.
Baruch Spinoza