In examining those arguments, they were necessarily led to consider the difference between a probable and a demonstrative argument, between a fallacious and a conclusive one; and logic, or the science of the general principles of good and bad reasoning, necessarily arose out of the observations which a scrutiny of this kind gave occasion to; though, in its origin, posterior both to physics and to ethics, it was commonly taught, not indeed in all, but in the greater part of the ancient schools of philosophy, previously to either of those sciences.