I am trying to analyze the following argument by Hume in his Treatise of Human Nature:
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: Wilful 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.
I am reconstructing it as:
- When examining willful murder, we find passions, motives, volitions and thoughts (in the murderer).
- This is an exhaustive list of the matter of facts of the crime.
- We did not find “vice” in the matter of facts of the crime.
- We find a sentiment of disapprobation towards the crime inside ourselves, as a matter of fact.
- That sentiment is a feeling, not reason.
- Conclusion: when we say that a murder is vicious, we express a subjective feeling.
However, it seems there is something slightly amiss about the term "vice" itself. It seems the argument actually defines vice in its conclusion (at least in my reconstruction), but that term was used in the third premise already, before being defined. How can we be sure we didn't find "vice" in the matters of fact of the crime, when in fact, what constitutes "vice" is defined later in the argument as a "sentiment of disapprobation"? Hume seems to use an implicit premise that we know how to recognize "vice" when we see it, or at least the absence of "vice" in the matters of fact of the murder, that we have at least some sort of shared intuition of what "vice" is (since we are not finding it). Hume seems to assume we can tell that there is no "vice", and furthermore that we will all agree on that. Should I add that hidden premise to my reconstruction to make the argument more cogent?
My question is really about 1) whether my reconstruction is right or misses that implicit premise about an immediate understanding of "vice"; 2) whether there is a logical defect in the argument, precisely because the term "vice" is used before being properly defined.