People must have renounced, it seems to me, all natural intelligence to dare to advance that animals are but animated machines.... It appears to me, besides, that such people can never have observed with attention the character of animals, not to have distinguished among them the different voices of need, of suffering, of joy, of pain, of love, of anger, and of all their affections. It would be very strange that they should express so well what they could not feel.
VoltaireWhat is called happiness is an abstract idea, composed of various ideas of pleasure; for he who has but a moment of pleasure is not a happy man, in like manner that a moment of grief constitutes not a miserable one.
Voltaire