UNDER THE APPLE-TREES 
grounds of physical certainty afforded by observa- 
tion and experience. There are only two kinds of 
proof, mathematical proof, and experimental or sci- 
entific proof. There is not, and cannot be, such a 
thing as metaphysical proof, because metaphysical 
truths are unconditioned — they are like a sea with- 
out shores or land without boundaries. We may 
feel them to be real and true, while another man 
may not feel them so at all. But the truths of sci- 
ence and mathematics are true to all men. To dis- 
pute them is to dispute weights and measures. A 
path through the fields seems a very real thing: see 
it winding on ahead of us; our feet can find it in the 
dark, but it is only a phantom, a negation, an ab- 
sence of something — a result of the attrition of 
many feet passing and repassing that way. Where 
are the tracks we made in last year’s snow? The 
snow was real, and still, in some form, exists; and 
the feet were real, and may still exist; but the track 
was only a shape in a material thing. 
In the printed page the only real things are the 
paper and the ink; the white spaces play the same 
part in aiding the eye to take in the meaning of the 
print as do the black letters. The type was real, and 
the mind and hands that shaped the type, and the 
compositor that set it up, were real, and the sense 
of the print is real to the mind, but not to the 
body. All this science affirms; what does philosophy 
affirm? 
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