Observation is the act of apprehending things and events, their attributes and their concrete relationships. From the point of view of scientific interest two types of observation may be distinguished, namely: (1) The bare observation of phenomena under conditions which are beyond the control of the investigator, and (2) experiment, that is, the observation of phenomena under conditions controlled by the investigator. What distinguishes experiment from bare observation is control over what is observed, not the use of scientific apparatus, nor the amount of trouble taken. The mere use of telescopes or microscopes, etc., even the selection of specially suitable times and places of observation, does not constitute an experiment, if there is no control over the phenomenon observed. On the other hand, where there is such control, there is experiment, even if next to no apparatus be used, and the amount of trouble involved be negligible. The making of experiments usually demands the employment of technical methods, but the main interest centres in the observations made possible thereby. The great advantage of experiment over bare observation is that it renders possible a more reliable analysis of complex phenomena, and more reliable inferences about their connections, by the variation of circumstances, which it effects. Its importance is so great that people commonly speak of "experimental method." The objection to this is that experiment may be, and is, used in connection with various methods, which are differentiated on other, and more legitimate, grounds. To speak of a method of observation is even less permissible, seeing that no method can be employed without it.
Analysis and Synthesis.
The phenomena of nature are very complex and, to all appearances, very confused. The discovery of any kind of order in them is only rendered possible by processes of analysis and synthesis. These are as essential to all scientific investigation as is observation itself. The process of analysis is helped by the comparison of two or more objects or events that are similar in some respects and different in others. But while comparison is a necessary instrument of analysis, analysis, in its turn, renders possible more exact comparison. After analysing some complex whole into its parts or aspects, we may tentatively connect one of these with another in order to discover a law of connection, or we may, in imagination, combine again some of them and so form an idea of what may be common to many objects or events, or to whole classes of them. Some combinations so obtained may not correspond to anything that has ever been observed. In this way analysis and synthesis, even though they are merely mental in the first instance, prepare the way for experiment, for discovery and invention.
Imagination, Supposition and Idealisation.
Such order as may be inherent in the phenomena of nature is not obvious on the face of them. It has to be sought out by an active interrogation of nature. The interrogation takes the form of making tentative suppositions, with the aid of imagination, as to what kind of order might prevail in the phenomena under investigation. Such suppositions are usually known as hypotheses, and the formation of fruitful hypotheses requires imagination and originality, as well as familiarity with the facts investigated. Without the guidance of such hypotheses observation itself would be barren in science for we should not know what to look for. Mere staring at facts is not yet scientific observation of them. Hence for science any hypothesis, provided it can be put to the test of observation or experiment, is better than none. For observation not guided by ideas is blind, just as ideas not tested by observations are empty. Hypotheses that can be put to the test, even if they should turn out to be false, are called "fruitful"; those that cannot be so tested even if they should eventually be found to be true, are for the time being called "barren." Intimately connected with the processes of imagination and supposition is the process of idealisation, that is, the process of conceiving the ideal form or ideal limit of something which may be observable but always falls short, in its observed forms, of the ideal. The use of limiting cases in mathematics, and of conceptions like those of an "economic man" in science are examples of such idealisation.