So far I have been speaking of theoretical science, which is an attempt to understand the world. Practical science, which is an attempt to change the world, has been important from the first, and has continually increased in importance, until it has almost ousted theoretical science from men's thoughts.
A science only advances with certainty, when the plan of inquiry and the object of our researches have been clearly defined; otherwise a small number of truths are loosely laid hold of, without their connexion being perceived, and numerous errors, without being enabled to detect their fallacy.