“Take any action allowed to be vicious; willful murder, for instance. Examine it in all lights, and see if you can find that matter of fact, or real existence, which you call “vice.” In whichever way you take it, you find only certain passions, motives, volitions, and thoughts. There is no other matter of fact in the case…
…In every system of morality which I have hitherto met with, I have always remarked, 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 surprised 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 of affirmation, it is necessary that it should be observed and explained; 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 wold 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 perceived by reason. ” (David Hume, Treatise of Human Nature, vol. II in the Philosophical Works of David Hume (Boston: Litttle, Brown , 1854), sec I, pt l, pp. 230-32.
The famous British philosopher of the early 20th century, G.E. Moore, also expotulated on what he called The Naturalistic Fallacy, which is going from an is to an ought.
Furthermore, the Logical Positivists of the 1920’s categorically declared moral statements meaningless, as simply expressions of emotion.
But consider the following reasoned argument from Thomas Reid, a contemporary of David Hume.
“All reasoning must be grounded on first principles. This holds in moral reasoning, as in all other kinds. There must, therefore, be in morals, as in all other sciences, first or self-evident principles, on which all moral reasoning is grounded, and on which it ultimately rests. From such self-evident principles, conclusions may be drawn synthetically with regard to the moral conduct of life; and particular duties or virtues may be traced back to such principles, analytically. But, without such principles, we can no more establish any conclusion in morals, than we can build a castle in the air, without any foundation. “
…Thus we shall find that all moral reasoning rests upon one or more first principles of morals, whose truth is immediately perceived without reasoning, by all men come to years of understanding. And this need is common to every branch of human knowledge that deserves the name of science. There must be first principles proper to that science, by which the whole superstructure is supported. The first principles of all the sciences, must be the immediate dictates of our natural faculties; nor is it possible that we should have any other evidence of their truth. And in different sciences the faculties which dictate their first principles are very different.
The first principles of morals are the immediate dictates of the moral faculty. They show us, not what man is, but what he ought to be. Whatever is immediately perceived to be just, honest, and honourable, in human conduct, carries moral obligation along with it, and the contrary carries demerit and blame; and, from those moral obligations that are immediately perceived, all other moral obligations must be deduced by reasoning.
He that will judge of the colour of an object, must consult his eyes, in a good light, when there is no medium or contiguous objects that may give it a false tinge. But in vain will he consult every other faculty in this matter. In like manner, he that will judge of the first principles of morals, must consult his conscience, or moral faculty, when he is calm and dispassionate, unbiased by interest, affection, or fashion. As we rely upon the clear and distinct testimony of our eyes, concerning the colours and figures of the bodies about us, we have the same reason to rely with security upon the clear and unbiased testimony of our conscience, with regard to what we ought and ought not to do. In many cases moral worth and demerit are discerned no less clearly by the last of those natural faculties, than figure and colour by the first.
…Every man in his senses believes his eyes, his ears, and his other senses. He believes his consciousness with respect to his own thoughts and purposes; his memory, with regard to what is past; his understanding, with regard to abstract relations of things; and his taste, with regard to what is elegant and beautiful. And he has the same necessity of believing the clear and unbiased dictates of his conscience, with regard to what is honourable and what is base…”
(from Thomas Reid: Essays on the Active Powers of Man, Essay III: Chapters V, VI and VII and Essay IV: Chapter IX, 1788.)
In this regard, A.C. Ewing, a 20th century philosopher, writes:
“…Probably the principal reason which makes people inclined to deny the objectivity of ethics is the fact that in ethical argument we are very soon brought to a point where we have to fall back on intuition, so that disputants are placed in a situation where there are just two conflicting intuitions between which there seems to be no means of deciding….
We must therefore have intuition, and in a subject where infallibility is not attainable, intuitions will sometimes disagree. Some philosophers indeed prefer not to call them intuitions when they are wrong, but then the problem will be to distinguish real from ostensible intuitions, since people certainly sometimes think they see intuitively what is not true. Now Lord Russell says: “Since no way can be even imagined for deciding a difference as to values, the conclusion is forced upon us that the difference is one of tastes, not one as to any objective truth.” (Bertrand Russell, Religion and Science).
(A.C. Ewing, The Definition of Good, 1947)