is created that these lines converge to
the right and diverge to the left. The vision is deceived in its mental
factor and judges wrongly of the thing seen.

In this case we are able to measure the distance of the lines, to find
how the main lines looked before the cross ones were drawn, to bring
the deception up against fact of a different sort and so correct the
mistake. If the ignorant observer were unable to do that, he might
remain permanently under the impression that the main lines were out of
parallelism. And all the infirmities of eye and ear, touch and taste,
are discovered and checked by the fact that the erroneous impressions
presently strike against fact and discover an incompatibility with it.
If they did not we should never have discovered them. If on the other
hand they are so incompatible with fact as to endanger the lives of
the beings labouring under such infirmities, they would tend to be
eliminated from among our defects.

The presumption to which biological science brings one is that the
senses and mind will work as well as the survival of the species may
require, but that they will not work so very much better. There is no
ground in matter-of-fact experience for assuming that there is any more
inevitable certitude about purely intellectual operations than there
is about sensory perceptions. The mind of a man may be primarily only a
food-seeking, danger-avoiding, mate-finding instrument, just as the mind
of a dog is, just as the nose of a dog is, or the snout of a pig.

You see the strong preparatory reason there is in this view of life for
entertaining the suppositions that:--

The senses seem surer than they are.

The thinking mind seems clearer than it is and is more positive than it
ought to be.

The world of fact is not what it appears to be.

1.5. THE CLASSIFICATORY ASSUMPTION.

After I had studied science and particularly biological science for some
years, I became a teacher in a school for boys. I found it necessary
to supplement my untutored conception of teaching method by a more
systematic knowledge of its principles and methods, and I took the
courses for the diplomas of Licentiate and Fellow of the London College
of Preceptors which happened to be convenient for me. These courses
included some of the more elementary aspects of psychology and logic
and set me thinking and reading further. From the first, Logic as it was
presented to me impressed me as a system of ideas