Others say, if there are many causes, each by itself becomes the cause of one thing. For instance, the virtues, which are many, are causes of happiness, which is one; and of warmth and pain, similarly, the causes are many. Are not, then, the many virtues one in power, and the sources of warmth and of pain so, also? and does not the multitude of the virtues, being one in kind, become the cause of the one result, happiness?