SCIENCE 7 



not all of the conditions are the same. Any difference in the results of 

 the two experiments can be attributed to these differences in the con- 

 ditions. The "control" thus provides a frame of reference by which the 

 results can be judged. More detailed information on the designing and 

 planning of experiments is included in several later chapters. 



Observ^ation is the source of new scientific information, but this infor- 

 mation is meaningful only if it is interpreted and meshed with what 

 is already known. The formation of explanatory statements is an equally 

 important part of scientific activity. The results of any single observa- 

 tion or experiment represent a small bit of information and may be use- 

 less alone. The scientist is likely to suggest, however, that the results 

 of the experiment are representative of a much larger body of informa- 

 tion. If the leaves of a plant grown without nitrogen turn yellow, perhaps 

 the leaves of all plants grown without nitrogen would turn yellow. Or, 

 to put it another way, perhaps all yellow leaves are the result of growth 

 without nitrogen. Either of these suggestions is a generalization founded 

 on little evidence, but each is at least reasonable. Inductive reasoning 

 has been used to arrive at an explanatory statement. Information from 

 a particular situation has been applied to the more general case. Ac- 

 tually, one cannot have much confidence in these suggestions, because 

 they result from only one experiment, and the two statements are rather 

 different from each other. Is one of them correct? Are both correct? 

 Each of these two suggestions must be called a hypothesis, a tentative 

 explanation based on some evidence. 



If the first hypothesis is correct, it should be reasonable to predict that 

 plants raised without nitrogen, even under somewhat different condi- 

 tions, should have yellow leaves. This type of reasoning is deductive; 

 a general statement is used to predict what will happen in a particular 

 set of circumstances. This new suggestion can be tested by performing 

 another experiment. If the prediction turns out to be correct, a new, 

 better generalization is in order, and further predictions can be made. 



You might have heard that science did not develop until Francis 

 Bacon suggested inductive reasoning. This statement is probably true, 

 but do not forget that science uses deductive reasoning too. 



Scientific method 



"Scientific method" is a term which has become distasteful to some 

 scientists. There are many "scientific methods," and the number of steps 

 and the order of the steps will depend upon the author of the list. Conant 



