what is to be known when it by chance strays
into the realm of conscious cognition. Any as yet unexplained exception
to an old theory can happen only in the experience of an individual, and
that which has its existence as an event in some one's biography is a
different thing from the future instance which is not beholden to any
one for its existence. Yet there are, as I indicated earlier, meanings
in this exceptional event which, at least for the time, are unaffected
by the exceptional character of the occurrence. For example, certain
clinical symptoms by which an infectious disease is identified have
remained unchanged in diagnosis since the days of Hippocrates. These
characters remain as characters of the instance of the law of
germ-origin when this law has been discovered. This may lead us to say
that the exception which appears for the time being as a unique incident
in a biography is identical with the instance of a germ-induced disease.
Indeed, we are likely to go further and, in the assurance of the new
doctrine, state that former exceptions can (or with adequate
acquaintance with the facts could) be proved to be necessarily an
instance of a disease carried by a germ. The positivist is therefore
confident that the field of scientific knowledge is made up of events
which are instances of uniform series, although under conditions of
inadequate information some of them appear as exceptions to the
statements of uniformities, in truth the latter being no uniformities at
all.

That this is not a true statement of the nature of the exception and of
the instance, it is not difficult to show if we are willing to accept
the accounts which the scientists themselves give of their own
observation, the changing forms which the hypothesis assumes during the
effort to reach a solution and the ultimate reconstruction which attends
the final tested solution. Wherever we are fortunate enough, as in the
biographies of men such as Darwin and Pasteur, to follow a number of the
steps by which they recognized problems and worked out tenable
hypotheses for their solution, we find that the direction which is given
to attention in the early stage of scientific investigation is toward
conflicts between current theories and observed phenomena, and that
since the form which these observations take is determined by the
opposition, it is determined by a statement which itself is later
abandoned. We find that the scope and character of the obse