In trying to understand why a chemist thought as he did, and drew one set of conclusions rather than another, probably the most important thing we need to know is what picture he had in mind of the way in which chemical reactions take place. There are, of course, many other things we need to know. For example, we need to know his social, economic and cultural circumstances, how he was educated and his ideas of the social function of science (...) and in particular of chemistry; we need to know what scientific societies and institutions he belonged to and how they influenced him; and we need to know what he hoped to get out of his work in chemistry—fame or a living or personal satisfaction or a combination of two or three of those results. Indeed, it has become fashionable in recent years to consider those aspects rather than the nature of his actual chemical thought. Yet in the end, his mental picture of chemical change is surely the most important factor in determining what the chemist's results will be, and is therefore the most important factor for historians to understand. (shrink)