As a general method of scientific study, correlation is partly a matter of both controlled and natural experiment, and partly one of classification. Soil science furnishes a good example. It is utterly unthinkable to set up experiments on all fields and farms to see what practices are best. But millions of farmers are already following different methods. By studying the growth of plants in unused areas and the results of experiments and farmer experience with various methods of soil use, in relation to defined sets of soil conditions, the scientist can gradually build up a set of principles with which he can make predictions about what will happen when a soil with any given set of characteristics is used in a particular way. Each soil with an individual set of characteristics is given a name for convenience. It is one unit in the system of classification. By comparing the set of characteristics of a new or unknown soil with those of soils already in the system, its name and place in the scheme of classification is determined.

The essential coordination for planning, conducting, and interpreting agricultural research in the United States is achieved largely through voluntary cooperation. During years of working together, arrangements have been evolved for cooperation among different kinds of scientists and between State and Federal research groups. The advantages of such cooperation are so obvious and so generally accepted among all thoughtful agricultural scientists, that a noncooperator soon loses the respect of his colleagues.

Both facts and ideas are essential to scientific inquiry. Often ideas come to the trained mind as flashes, as new combinations of principles in the mind. As facts are obtained to test the idea, it may be found to be wrong; for every success, the scientist has many failures. Or it may take form and become more precise. The scientist then draws a tentative conclusion, which, if true, means that other things are true. These he sets out to test. The results of the new research may lead to the results he expected and confirm the idea, or perhaps to something quite different. Then he must revise his original notion. In this way facts lead to ideas, ideas to more facts, these to revised or new ideas, and so on. The process never ends.

Among modern scientists, the place of the lone worker is becoming smaller. The larger part of our problems requires many people with different skills, working together. Nevertheless, efficiency of organization to get facts must not be allowed to stifle ideas or to lull the individual scientist into the complacency of a cogwheel. A perfect scientific research organization, with all responsibility clear, with each man in his proper niche, and with no overlapping or duplication, might be a bureaucrat's dream—but it would be an empty one. Scientific research requires the flashes of the human mind. They are like lightning; we cannot know where they will strike or how. Scientists need to organize themselves in ways to get the advantages of group research without losing the essential freedom of the individual researcher.

Free criticism is essential to science. People get ideas, test them, and improve them with experience. The same may be said of a functioning democracy. Thus are the scientific method and the democratic process similar. Of course, scientific questions cannot be settled by voting in committees. We can only say that the scientific truth currently accepted is what informed scientists say it is—their present opinion. No man has been granted the gift of absolute knowledge, and scientists are men. But free publication by the scientist and free criticism by his peers—his informed colleagues—are essential to the scientific method. No man can be trusted to speak with authority without such criticism. He is too close to his own ideas to see them whole, no matter how hard he tries.

Our society is becoming more and more dependent upon science. Scientists must be supported in their work and their opinions must be respected. But they are human, subject to all the vanities and fears of other men. Some are good workmen and honest ones; others are not. There can be no absolute guide to tell us whom to believe. Even the scientist himself is a layman in most fields. If he simply uses the special techniques of his own field without undertaking the deeper meaning of the scientific method as applied generally, he may be as blindly dogmatic or as bad a dupe as anyone in other fields. We can ask these questions about a scientist: Has he sincerely and competently followed the scientific method? Is he free to tell the truth as he sees it—free of personal prejudices and of political or social pressure? Has his work been tested by free and open criticism? Has he the respect (not necessarily personal friendship) of competent colleagues in the same field? If the answer to any of these questions is "No," we should be slow to believe him.

Agricultural scientists work mostly in public institutions; only a few are supported by private industries or groups of farmers. This is because farming is mostly carried on in small units that would find it hard, even in combinations, to undertake research, and because most problems of agriculture involve so many skills that even a group of minimum size for effective work requires considerable land, buildings, and equipment. Besides, effective educational and demonstration programs must be closely allied with the research activity if farmers are to benefit from the results.

For more than 75 years most agricultural research in this country has been carried on by the United States Department of Agriculture and the State land-grant colleges. Nevertheless, the great importance of other institutions carrying on research in the basic sciences should not be Overlooked.