The distinction is of importance in many
ways, and not least as a means of avoiding heat in argument; for to
question a man's inference is much less likely to make him angry than to
deny his statement of fact.

For the practical purposes of argument we may let the distinction
between observation and inference, and consequently that between direct
and indirect evidence, turn on whether the inference is a conscious and
readily distinguishable part of the judgment or not. Though bringing to
light an unconscious inference is often an essential part of the
detection of false reasoning, where there is no such practical
consequence, we need not be too curious here about the line between
direct observation and inference from observation. For the rough and
ready purposes of everyday arguments it is exact enough to say that
where you recognize that you are basing your conclusion as to a fact on
some process of reasoning, then you are resting on indirect evidence;
where you do not recognize the inference without reflection, you are
resting on direct evidence.

In the following discussion of reasoning I shall sometimes be dealing
with proving a fact, sometimes with arguing forward to a policy. In many
cases the two processes are practically identical, for if the fact is
established the policy follows as a matter of course: in these cases,
therefore, for the sake of convenience I shall use the terms
interchangeably, and keep them separate only where there is danger of
confusion.

33. Reasoning. Though the various forms of reasoning and the
principles which they follow are the concern rather of psychology and
logic than of a practical work on the writing of arguments, yet these
sciences help us to understand the processes of the mind by which we
convince first ourselves, and then other people, of the existence of
facts, when for one reason or another direct testimony is wanting.
Psychology describes the processes of reasoning as part of the activity
of the mind, analyzes them into their parts, and shows their working.
Logic is concerned rather with the forms of reasoning: its aim is to
establish principles and rules the application of which will insure
correct reasoning.

I shall first briefly and very simply sketch the underlying nature of
the reasoning process as it is described by psychologists; then I shall
pass on to a practical application of the principles thereby attained;
next I shall set forth a few of the simplest an