Artificial values, according to Hume are the bedrock of his view on justice with regards to his moral philosophy. They are integral to his thinking as they demonstrate how we can develop our virtuous code beyond that which is given us from nature itself and become a society of civil and organised nature. Indeed, it seems for Hume that without such artificial virtues we would be an inherently selfish race, with little to bind us in a coherent social body.
To understand what Hume means by artificial virtues we must first assess what he considers to be a virtue in essence. Taken at its most basic form, a virtue is moralÂ excellence, a character trait or qualityÂ valuedÂ as beingÂ good.
Personal virtues are characteristicsÂ valuedÂ as promoting individual and collective well-being, and thusÂ goodÂ by definition. The opposite of virtue isÂ vice.
Hume identifies two such occurrences of virtue, the first of which are natural virtues. It is integral that one understands the distinction between this set of virtues and that of artificial virtues before we can begin to explore why Hume may value artificial virtues so highly, and why indeed they are discernable from virtue as a whole.
Hume describes Natural virtues as virtues that we, as a human race, have in a natural environment without the edifices of society surrounding us. Indeed, they are such values that we would have in an environment completely free from social structures such as government, a system of judicial law or a monarch. It can be seen that Hume takes ideas such as Thomas Hobbes' State of nature to develop his ideas, Hobbes presenting a hypothetical existence of humanity in which we exist as solely individual beings without any social constraints or covenants  , and Hume using it to understand what kind of virtues we might possess in such an environment.
Hume posits that such 'natural virtues' would be such things as having mercy, loving one's own life, and being benevolent to children as a means to further the human race as a species. Most importantly, these are virtues that people have independently of society. These virtues produce certain actions and as we call them virtues, we approve of these actions.
Thus we have a referential definition to identify what Hume would denote as a natural virtue, in other words a virtuous character trait that one could conceivably hold in one's person without the need of deterrents and incentives introduced by a civilised society or state. The traits he calls natural virtues are more refined and completed forms of those human sentiments we could expect to find even in people who belonged to no society but cooperated only within small familial groups.
By reasoned thinking then, artificial values must be the contrasting notion, the other side of the coin, so to speak. Indeed Hume notes that to have an artificial virtue is to have a virtue developed purely as a result of the state and social conventions, be they enforced or not, around you. Hume emphasises this in the treatise on Human nature, stating that "our sense of every kind of virtue is not natural; but â€¦ there are some virtues, that produce pleasure and approbation by means of an artifice or contrivance, which arises from the circumstances and necessities of mankind"  The traits he calls artificial virtues are the ones we need for successfulÂ impersonal cooperation; our natural sentiments are too partial to give rise to these without intervention. In theÂ TreatiseÂ Hume includes among the artificial virtues honesty with respect to property (which he often calls equity or "justice," though it is a strangely narrow use of the term), fidelity to promises (sometimes also listed under "justice"), allegiance to one's government, conformity to the laws of nations (for princes), chastity (refraining from non-marital sex) and modesty (both primarily for women and girls), and good manners. 
In some ways, this can be seen to lead us to the next point of discussion, that of why these artificial virtues prove of such importance for Hume and his moral philosophy. Having established Hume's outlook and theoretical background to what constitutes an artificial value, we can see that one of the most potentially important of these is that of 'justice'. Hume argues that , while not immediately apparent, the difference between the natural virtues and justice lies in that the good, which results from the former, arises from every single act, and this is the object of some passion: whereas a single act of justice, considered in itself, may often be contrary to the public good  . The value of justice as an artificial value cannot be overlooked, states Hume, referencing the reasoning why it appears a society without the artificial values it constitutes would collapse. For example, Hume discusses two stances, that of limited generosity and scarcity of resources to exemplify just how indispensable artificial values and in particular, justice, can be to maintaining order, control, and a manner of living in social harmony.
Through limited generosity, he claims that people have natural values of benevolence but they are not sufficient to explain behaviour that we would call just  . In other words, while he sees humans as having natural virtues that lead us towards a path of benevolence and a general acquiesce to a code of not obstructing the happiness of others, they are not sufficient alone to constitute a system of values where resources and actions are to be always deemed fair and equal. Obviously for a moral system of reasoning this is an avoidable circumstance if possible, thus further highlighting the importance of artificial values in Hume's line of thought.
Furthermore, the scarcity of resources that would exist in a world of purely natural values, postulates Hume, would also cause social upheaval and potentially cause an obstruction to the pursuit of the good. Combine a lack of resources with limited generosity, and a situation will arise where not every person can be guaranteed their fair share. Without justice then, one cannot hope to avoid conflict entirely as various individuals will begin to query their lot in some given arrangement.
Justice, with its ability to provide a deterrent to those with a inclination to incite disharmony is thus incredibly important to Hume, and plays a vital role as an artificial virtue.
However, it is not alone in demonstrating the need for artificial virtues as a whole. Hume continues in the Treatise to suggest that the virtues of material honesty and of faithfulness to promises and contracts, both obviously necessary to hold together the conventions of what is deemed a normal society, are artificial, not natural virtues. Hume refers to these kinds of artificial values with an inclusive term known as conventions, and these emerge to deal with circumstances of limited generosity and scarcity which produce stable relations between people and from which in the end everyone can benefit. Such conventions develop slowly argues Hume, using the example of two men pulling on the oars of a boat: Two men who pull on the oars of a boat do it as a convention but they have not made promises to each other. Such a convention arises gradually and acquires force by slow progression, and by our repeated experience of the inconvenience of transgressing it  .
Hume then sports artificial virtues to be those which develop, not in us naturally, but arise from the structures of civilised society. However, what actually makes them important in Hume's moral philosophy and appropriates them as integral to creating a harmonious moral society is the individual virtues that Hume categorises as artificial, as opposed to the concept of them as a collection. While Hume discusses several, such as conventions to fulfil promises and recognition of property, arguably the most key is that of justice. While it is an abstract notion in itself, Hume clearly believes it to be one of the most established pillars of society, leading the creation of conventions that bind us in a code of conduct deliberating us from vice. The importance of artificial virtues therefore lies in their ability to separate us from the categorically unsociable creatures tentatively explored in a hypothetical world of purely natural virtues, and the world of sociable civilised humans we recognise and embody in corporeal existence.