rning to the parlor of your house, finds that a
tea-pot and some spoons which had been left in the room on the previous
evening are gone,--the window is open, and you observe the mark of a
dirty hand on the window-frame, and perhaps, in addition to that, you
notice the impress of a hob-nailed shoe on the gravel outside. All these
phenomena have struck your attention instantly, and before two seconds
have passed you say, "Oh, somebody has broken open the window, entered
the room, and run off with the spoons and the tea-pot!" That speech is
out of your mouth in a moment. And you will probably add, "I know there
has; I am quite sure of it!" You mean to say exactly what you know;
but in reality you are giving expression to what is, in all essential
particulars, an hypothesis. You do not KNOW it at all; it is nothing but
an hypothesis rapidly framed in your own mind. And it is an hypothesis
founded on a long train of inductions and deductions.

What are those inductions and deductions, and how have you got at this
hypothesis? You have observed in the first place, that the window
is open; but by a train of reasoning involving many inductions and
deductions, you have probably arrived long before at the general
law--and a very good one it is--that windows do not open of themselves;
and you therefore conclude that something has opened the window. A
second general law that you have arrived at in the same way is, that
tea-pots and spoons do not go out of a window spontaneously, and you are
satisfied that, as they are not now where you left them, they have been
removed. In the third place, you look at the marks on the windowsill,
and the shoe-marks outside, and you say that in all previous experience
the former kind of mark has never been produced by anything else but
the hand of a human being; and the same experience shows that no other
animal but man at present wears shoes with hob-nails in them such as
would produce the marks in the gravel. I do not know, even if we could
discover any of those "missing links" that are talked about, that they
would help us to any other conclusion! At any rate the law which states
our present experience is strong enough for my present purpose. You next
reach the conclusion that, as these kind [89] of marks have not been
left by any other animal than man, or are liable to be formed in any
other way than a man's hand and shoe, the marks in question have been
formed by a man in that way. You have, fur