In science, on the other hand, the assumption that we know what meanings our terms can convey is not made as a matter of course. We may begin with roughly labelling objects of interest, and then inquiries may be conducted into, e.g., ‘electricity’, ‘elements’, ‘life’, ‘species’, &c., in the hope of settling what these terms _shall_ mean, and of finding out _more_ about their meaning, and without making the assumption that whatever new facts are discovered about them must conform to our preconceptions and confirm our nomenclature. Thus to a man of science it will not be cogent to argue that because an ‘element’ is (by definition) an ultimate form of matter which cannot be broken up, and ‘radium’ breaks up, ‘radium’ is not an ‘element’, or that because ‘species’ are eternal forms, and the Darwinian theory claims that they are not immutable, it can be dismissed as involving the ‘contradiction’ that a ‘species’ is not a species. Thus the best syllogisms lose their cogency so soon as a question is raised whether the verbal identity of their terms is an adequate guarantee of the real identity of the things they are applied to. § 9. (3) It is a further presupposition of the logician’s conception of ‘proof’ that absolute truths exist, and that in the ideal demonstration they form the premisses from which the conclusion follows. This presupposition is not stated, and is not implied in the form of the syllogism. For a syllogism is no less ‘valid’ if its premisses are true only hypothetically, and not absolutely. Indeed, it is not thought to impair the ‘validity’ of a syllogism that its premisses should be utterly false. At any rate we can _reason_ quite as well with hypotheses and probabilities as with absolute truths, and this is in fact what we usually do, whether or not we are aware that our premisses are conditional and hypothetical. This ordinary practice, however, is resented by the traditional logic. For if our premisses are only hypothetically true, how can they lead to conclusions which can be declared absolutely true? And if our conclusions are not absolutely true, how can they be certain? Are they not bound to remain infected with the doubts which beset their premisses?[383] As we value the certainty of our conclusions, therefore, absolutely true and certain premisses must be procured. If they cannot be procured, even the best formal proofs will remain hypothetical, and all truth will become dependent on experience. For if nothing is true absolutely, and every truth has originated humbly in a guess that has grown into a successful hypothesis, it can always be suggested that after all it may benefit by a little more verification. It may be true enough psychologically and for practical purposes, but it does not realize the ideal of ‘logical certainty’.