IV.  Next, on what subjects and to what extent may we philosophize?  On matters within our reach, and to such an extent as the mental power and grasp of our audience may extend.  No further, lest, as excessively loud sounds injure the hearing, or excess of food the body, or, if you will, as excessive burdens beyond the strength injure those who bear them, or excessive rains the earth; so these too, being pressed down and overweighted by the stiffness, if I may use the expression, of the arguments should suffer loss even in respect of the strength they originally possessed. i.e. Should not only fail to be strengthened thereby, but be actually weakened, through their inability to understand the argument.  A bad defence weakens a good cause.