For it is clear that the soul's modes are changeable but ideas are immutable; that its modes are particular, but ideas are universal and general to all intelligences; that its modes are contingent, but ideas are eternal The Search after and necessary; that its modes are obscure and shadowy, but ideas are very clear and luminous (i.e., its modes are only obscurely, though vividly, felt, but ideas are clearly known as the foundation of all the sciences); that these ideas are indeed efficacious because they act in the mind, they enlighten it and make it happy or unhappy, which is evident by the pain