234 PHILOSOPHY OF ZOOLOGY. 
the same event shall take place in the same circumstances ; 
but when there is any change in the circumstances, we ex- 
pect the event with less certainty, and our confidence is 
weakened with the extent of the change. 
(b.) Testimony.—Experience is the result of our own 
efforts to attam truth: Testimony is the medium by which 
we become acquainted with the knowledge or truth of 
others. Our confidence in the truth of the testimony of 
others, depends on its conformity to our own experience, 
and the usual agreement of facts with the report of witnes- 
ses. Besides, the signs which we generally employ, repre- 
sent the ideas which we have formed, and we suppose that 
others employ signs in the same manner. 
In early life, we give ready assent to any statement, be- 
cause, not being aware of the difficulties of ascertaining the 
truth, and ignorant of the process of dissembling, we draw 
conclusions from the testimony of others, in the same hasty 
and incautious manner as we do from the evidence of our 
own senses. 
When experience has convinced us that our senses fre- 
quently give us false information, we become more cautious 
in admitting the evidence of others, until we are satisfied 
that they were not deceived. 
In the course of our experience, we find that false ap- 
pearances deceive ourselves, and, from various causes, we 
perceive that they are employed to deceive others. ‘The na- 
tural result of this information, is a diffidence in testimony, 
until we are satisfied that there is xo attempt to deceive. 
Still more extensive experience and reflection strengthen the 
diffidence, by making us acquainted with the ambiguity of 
the signs which are employed in communicating the expe- 
rience of others. | 
When once we are satisfied that, having guarded against 
all sources of error, we have -ascertaned the truth, no ops 
