Douglas Thomson

I cannot forbear adding to these reasonings an observation, which may, perhaps, be found of some importance. In every system of morality, which I have hitherto met with, I have always remark'd, that the author proceeds for some time in the ordinary way of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when of a sudden I am surpriz'd to find, that instead of the usual copulations of propositions, is , and is not , I meet with no proposition that is not connected with an ought , or an ought not. This change is imperceptible; but is, however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, 'tis necessary that it shou'd be observ'd and explain'd; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it. But as authors do not commonly use this precaution, I shall presume to recommend it to the readers; and am persuaded, that this small attention wou'd subvert all the vulgar systems of morality, and let us see, that the distinction of vice and virtue is not founded merely on the relations of objects, nor is perceiv'd by reason

The question is raised whether there are forms of reasoning peculiar to philosophy. But if one considers what has been written over the centuries in the name of philosophy, it hardly seems possible that there is any form of ‘reasoning’, however widely one uses that word, which has not been employed. Formal deductive reasoning, appeals to empirical data, arguments from the way in which language is used, arguments from analogy—it is not difficult to think of examples of all of these and more. How effectively or successfully they have been used is, of course, another matter.