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I have assumed that a science of historical criticism ought to 
exist. It may be defined as the science which discriminates 
between fact and fiction in the history of the past. If there be 
no such science, we can have no certain grounds for knowing what 
is true or false in the events of history, and past experience would 
be rendered worthless as a guide to the future. No less dan- 
gerous is the introduction into it of false principles, by which 
whole regions of fact are consigned to the domains of fiction. 
The most dangerous attacks on Christianity have originated in 
false principles of historical criticism. 
I. One of the most important questions connected with this 
subject is the limit which ought to be assigned to what Professor 
Tyndall has designated the principle of philosophical imagina- 
tion ; or, to speak in the language of this science, the principle 
of historical conjecture. I put the case thus : if facts are 
deficient, or their evidence or interpretation uncertain, to what 
extent are we at liberty to supply the deficiency by the use of a 
supposed power of historical divination. You are aware that 
this principle has of late years claimed the right of reigning 
over a wide range of subjects, and pronouncing on them with 
dogmatical authority. Not only has it claimed the right of 
interpreting the mythical and semi-mythical periods of history 
with a boundless license of imagination, but within the historical 
period, where facts are separated from each other by an un- 
known void, many writers of history claim to possess the power 
of erecting a solid bridge of fact over the interval which separates 
the one from the other. I fully admit that it is both the right and 
the duty of those who engage in these inquiries to employ all the 
resources of reason in endeavouring to separate the true from 
the false in the history of the past ; but by this process there is 
no little danger that a number of mere conceptions which are 
merely subjective should become metamorphosed into objective 
facts. 
I am far from wishing to deny the use of philosophical 
imagination or historical conjecture, as long as they are kept 
within the limits which a sound philosophy will assign them. 
Without imagination all discovery is impossible ; but, like all 
other good gifts, it requires to be carefully watched, lest it 
should intrude itself beyond its legitimate province. Its duty is 
to act as the pioneer of reasoning, not to supply its place. Its 
unguarded use is far more dangerous in history than in science. 
Scientific analysis can subject its conjectures to a rigid verifica- 
tion ; and they have no right to plant themselves as facts on 
the solid earth until they have passed through this process. 
But as history treats only of the past, conjecture is incapable 
of verification, except by analogy ; its conclusions, therefore, 
