You hear about “justice” every day: SJWs demanding that straight white men be burned at the stake for “social justice”, different victims or criminals becoming the focus of “justice for this guy” mobs, in the statist prayer “liberty and justice for all”, justice in music, television, movies, lectures, C-span, everywhere. Reading Plato, one sees justice presented as “giving to everyone what they are owed” which is often interpreted through the lenses of “an eye for an eye” and “repay your debts”. Something often addressed alongside justice, and often used to help define the limits of justice, is mercy. People point to the beautiful occasions in which someone forgives the man who killed that person's entire family or something and say “faith in humanity: restored”. Christians, inspired by Thomism, love to juxtapose mercy and justice as opposites and then struggle to argue that God can simultaneously possess two opposites to an infinite degree, which is simply absurd.
“Blasphemy!” No, not really. It is the very definition of absurdity to simultaneously hold that both A and non-A are true. No amount of special pleading (mystery) or symbolic logic can change that. I'm not saying God isn't infinitely merciful or just, only that Aquinas made yet another mistake. As a matter of fact, I'm dropping this God talk in favor of philosophical exploration of justice and mercy themselves. Those of my readers that are both intelligent and theologically-minded will be able to follow this line of thought to its necessary conclusion concerning God's nature.
Most people, as I understand it, believe that justice is either some formless and vapid idea like “equality” or “fairness” or that it means “retribution”. “This guy did something bad, so we have to do bad things to him.” Very few people will argue with that description, only the specific reason for or implementation of it. “That guy raped someone, so we must lick him in a rape cage (prison) for the rest of his life.” “This lady stole some money, so we must take everything she owns or earns until it is paid back... and a little off the top for me.” There's always arguments as to how far is too far, like the death penalty; “should we murder a murderer?” but rarely is the more fundamental question asked.
Is doing “evil” to “evildoers” justice?
I'll leaver that question for your rumination while I address mercy. In the ancient world, mercy was a vice that only the most powerful could afford. In the Christian world, it was a benevolent act that even the most impoverished peasant could perform towards even the most powerful king. In the post-Christian world, it's a meaningless feel-good word for being nice. In each of these eras, the meaning of mercy has been assumed to mean “staying the execution of justice.” Debt forgiveness, governor pardons, jury nullification, victims and their families forgiving criminals, for example. Mercy, then, is shown by those too helpless to extract retribution on those with power. The paradigm case would be millennial SJWs getting jobs and shutting up.
Of course these two concepts are at odds. If justice has been a perennial issue of rights, honor, and morality throughout recorded history and mercy has been a more recent afterthought, it is no wonder that so many are confused, There are lots of exciting logical conundrums which emerge with this juxtaposition of two aesthetically pleasing opposites. I'm not sure I need to explore them right now, as everyone has read a book or watched a movie which hinged on one such conundrum or another. Any Christian that hasn't wrestled with these problems has not critically assessed their faith. It's a very real concern: when does one do evil to evildoers and when does one forgive them? I believe I have a solution. I'm not about to take credit for it, as the inspiration at least comes from the first couple centuries AD.
Our understanding of justice and the function it serves is wrong. Mercy, then, is also misunderstood, due to its status as wholly dependent on justice for its meaning. If justice is people getting what they deserved, people ought to do their best to keep their distance from me; as I've mentioned in a recent Daily Resource Suggestion, “Nobody deserves anything. If we deserve anything, it is nothingness.” Unsurprisingly, this is a Catholic belief; that's why theologians are so desperate to make God merciful.
I have intentionally avoided discussing justice from the utilitarian position, as they equivocate justice with political ethics: “Whatever laws and violence are shown to maximize pleasure for the most people, except the obvious answer of 'none'.” “Justice” as “deterring crime through punishing those that break the law” is a subset of the utilitarian stance. I call it moral/legal equivalence, and that's all the time I want to waste on it today.
If justice is not retribution or deterrent, if it's not repaying debts and taking an eye for an eye, what is it? If mercy is not the suspension of justice, what is mercy? Justice is restoration, and it is growth. Mercy is the proper application of justice. Doesn't make sense? Good.
Justice exists betwixt individuals. If one were to exist alone in the universe, there would be no party for him to injure or be injured by, there would be no party to establish or show justice to. In this way, justice is a concept that is only manifest between individuals. If one is injured by another, whether it be the intentional commission of a crime or an unintentional destruction of property or honor, their relationship is also damaged. If justice were merely returning harm for harm, both parties are rendered worse off than before the execution of justice and their relationship is damaged doubly so. If justice were merely the replacement of damaged goods, justice could not be applied in circumstances in which the damage is incalculable or immaterial such as the loss of a child or the stripping of honor. Justice (or mercy) could not merely be the forgiveness of transgressions between individuals, as whatever harm has been affected is still present and the relationship will remain damaged after the initial act of forgiveness.
Justice, if restorative, would require the growth of all parties involved. If one party were to be harmed by another, for both the property damaged and the relationship between individuals weakened, they must grow beyond the damage done. Harm itself is contrary to growth, even if it allows at times for growth that would have been otherwise impossible, so returning harm for harm is not justice. The replacement or repayment for damaged goods can be incorporated into an act of justice, as it is an attempt at restoring the status of things to their original state. As mentioned above, though, such an action alone cannot be justice and such an action may be impossible as some things are irreplaceable and relationships cannot return to previous states. The same goes for forgiveness, it is necessary but not sufficient for restoration of relationships and statuses.
The specific implementations of justice are contingent upon the circumstances of the injury between parties. What is required to grow beyond a stranger scuffing someone's shoe is orders of magnitude lesser than what is required to grow beyond a friend or family member murdering one's family with a chainsaw. In the first instance, a more sincere apology and offer to make amends and a subsequent act of forgiveness and re-polish or replacement of the shoes (by either party) is all that is required. In the latter case, the one concerning a murder most foul, I know not by what means one would grow beyond the loss of one's family nor if a relationship could be restored after such an inhuman crime, and I hope never to discover the answer.
Such a limitation is not a limitation of justice, but of those that ought to pursue it. Justice is one of the greatest expressions of discipline and the quintessential foundation of community for, without the mutual guarantee of justice, individuals are left to their own Hobbesian devices, unable to even raise a family. This is mercy, the manner in which justice can restore peace, community, and flourishing, how justice allows the growth of community despite the spectre of risk and bad actors.
Clearly, there is a tension between justice and self-defense. If I am obligated to defend myself, my autonomy, and my property at all costs, how can justice be applied once my assailant is dispatched? In some ways, it cannot; whatever relationship my assailant and I had is severed the moment he chooses to commit a crime against me, and it cannot be restored once he is dead. This tension ought to serve as a reminder to avoid exposure to crime and to encourage one to attempt de-escalation before resorting immediately to violence when someone is being an asshole.
TL;DR: Justice is not punishment, nor is it getting even. The only logically consistent description of justice is that it is restorative. Justice is a mutual concession of guilt and effort to grow beyond damages caused. There are limit cases to justice that can and ought to be explored, but first principles and the immediate fallout of those principles ought to be explored first, especially because this understanding of justice has been largely ignored in modern culture.