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 and clearest of the processes of reasoning which have been worked out by logic; and, finally, I shall discuss each few of the best-recognized forms of false reasoning.  From both the psychological description and the rules of logic we shall derive practical suggestions for establishing facts which may be needed in an argument.

The essential feature of the process of reasoning is that it proceeds from like to like, by breaking up whole facts and phenomena, and following out the implications or consequences of one or more of the parts.[24] For example, if I infer, when my dog comes out of a barnyard with an apologetic air, and with blood and feathers on his mouth, that he has been killing a hen, I am breaking up the whole phenomenon