"Whoever builds his faith exclusively on demonstrative proofs and deductive arguments, builds a faith on which it is impossible to rely. For he is affected by the negativities of constant objections. Certainty(al-yaqin) does not derive from the evidences of the mind but pours out from the depths of the heart."

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People say the effect is only on the mind. It is no such thing. The effect is on the body, too. Little as we know about the way in which we are affected by form, by color, and light, we do know this, that they have an actual physical effect. Variety of form and brilliancy of color in the objects presented to patients, are actual means of recovery.

— Florence Nightingale