explain the core of this text: I
 would fain ask any one, why incest in the human 
species is criminal, and why the very same 
action, and the same relations in animals have 
not the smallest moral turpitude and deformity? If 
it be answered, that this action is innocent in animals, because they have not reason sufficient to 
discover its turpitude; but that man, being endowed 
with that faculty which ought to restrain him to his 
duty, the same action instantly becomes criminal to 
him; should this be said, I would reply, that this is 
evidently arguing in a circle. For before reason can 
perceive this turpitude, the turpitude must exist; and 
consequently is independent of the decisions of our 
reason, and is their object more properly than their 
effect. According to this system, then, every animal, 
that has sense, and appetite, and will; that is, every 
animal must be susceptible of all the same virtues 
and vices, for which we ascribe praise and blame 
to human creatures. All the difference is, that our 
superior reason may serve to discover the vice or 
virtue, and by that means may augment the blame 
or praise: But still this discovery supposes a separate 
being in these moral distinctions, and a being, which 
depends only on the will and appetite, and which, 
both in thought and reality, may be distinguished 
from the reason. Animals are susceptible of the same 
relations, with respect to each other, as the human 
species, and therefore would also be susceptible of 
the same morality, if the essence of morality consisted in these relations. Their want of a sufficient 
degree of reason may hinder them from perceiving the duties and obligations of morality, but can 
never hinder these duties from existing; since they 
must antecedently exist, in order to their being perceived. Reason must find them, and can never produce them. This argument deserves to be weighed, 
as being, in my opinion, entirely decisive.
Nor does this reasoning only prove, that morality consists not in any relations, that are the objects 
of science; but if examined, will prove with equal 
certainty, that it consists not in any matter of fact, 
which can be discovered by the understanding. This 
is the second part of our argument; and if it can be 
made evident, we may conclude, that morality is 
not an object of reason. But can there be any difficulty in proving, that vice and virtue are not matters of fact, whose existence we can infer by reason? 
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 which-ever way you take it, 
you find only certain passions, motives, volitions 
and thoughts. There is no other matter of fact in the 
case. The vice entirely escapes you, as long as you 
consider the object. You never can find it, till you 
turn your reflection into your own breast, and find 
a sentiment of disapprobation, which arises in you, 
towards this action. Here is a matter of fact; but it 
is the object of feeling, not of reason. It lies in yourself, not in the object. So that when you pronounce 
any action or character to be vicious, you mean nothing, but that from the constitution of your nature you 
have a feeling or sentiment of blame from the contemplation of it. Vice and virtue, therefore, may be 
compared to sounds, colours, heat and cold, which, 
according to modern philosophy, are not qualities in 
objects, but perceptions in the mind: And this discovery in morals, like that other in physics, is to be 
regarded as a considerable advancement of the speculative sciences; though, like that too, it has little or no 
influence on practice. Nothing can be more real, or 
concern us more, than our own sentiments of pleasure and uneasiness; and if these be favourable to 
virtue, and unfavourable to vice, no more can be requisite to the regulation of our conduct and behaviour.
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 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 surprized 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, 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 would 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