While there are almost as many definitions of history as there are historians, modern practice most closely conforms to one that sees history as the attempt to recreate and explain the significant events of the past.
He chooses, when he can, the method of the “controlled experiment”. If he wants to find out the effect of light on growing plants, he takes many plants, as alike as possible. Some he stands in the sun, some in the shade, some in the dark, all the time keeping all other conditions (temperature, moisture, nourishment) the same. In this way, by keeping other considerations constant, and by varying the light only the effect of light on the plants can be clearly seen. This method of using “controls” can be applied to a variety of situations, and can be used to find the answers to questions as widely different as “Must moisture be present if iron is to rust?” and “Which variety of beans gives the greatest yield in one season?”