"Many chemists, even at the present day, find it impossible to do without certain collective names, analogous to the word phlogiston, for processes which they regard as belonging to the same class, or determined by the same cause. But instead of choosing for this purpose words which designate things, as was the custom till the end of the seventeenth... century, (phlogiston means, for example, fire, or light, and heat), they employ, since the time of Berthollet, terms which designate what are called "forces.""