§ 80. _Mens sana in corpore sano_ is correct as a pedagogical maxim, but
false in the judgment of individual cases; because it is possible, on
the one hand, to have a healthy mind in an unhealthy body, and, on the
other hand, an unhealthy mind in a healthy body. To strive after the
harmony of soul and body is the material condition of all proper
activity. The development of intelligence presupposes physical health.
Here we are to speak of the science of the art of Teaching. This had its
condition on the side of nature, as was before seen, in physical
Education, but in the sphere of mind it is related to Psychology and
Logic. It unites, in Teaching, considerations on Psychology as well as a
Logical method.