The Question and Its Importance
I was reading through Will Durant’s book The Story of Philosophy. The book is divided into sections on what the author considers to be the development of western philosophy. The first section covers Plato and his Republic, where the author writes of Plato and his style of asking questions, that “Nothing is so difficult as definition, nor anything so severe a test and exercise of mental clarity and skill." 
The author had mentioned earlier (but I can’t for the life of me find where he wrote it) something along the lines that philosophy exists to answer major questions such as, What is justice? What is truth? What is beauty?

I thought, as probably most of us do, that while I might not be able to define justice exactly, I know it when I see it. Or maybe more to the point, I know when I see INjustice. But nonetheless, I thought it would be a good exercise to answer some of the these questions. Truth I have a more succinct working definition of, and beauty is notoriously hard to pin down. But I’d never really thought too deeply about justice.   
Justice is a big topic these days. We hear slogans such as "No Justice, No Peace”, and calls for “Educational Justice”, “Climate Justice”, “Health Justice” and the like. What do those mean, and what should we be aiming for when we want to see “justice”?

It would be fundamental and necessary to establish what we mean by justice before we attempt to put policies in place that would purportedly guide us towards such a thing.

Justice in the Positive
Trying to work from just my own thoughts, and attempt a first principles approach: justice is a principle of being just. Justice is often thought of in the negative sense- such as what to do when someone does something that would violate justice. We have a justice system- which is primarily concerned with “maintaining” justice- as in meting out punishment when someone does what is unjust.

However, justice in the positive sense would seem to be something like fairness. Obviously we don’t steal stuff that isn’t ours, since we didn’t earn it, and taking it from someone else would be unfair, and therefore unjust. The question does seem to come up as to whether justice only comes into play inter-relationally. Would justice even be a concept if it weren’t between people?  

If I were to imagine myself living on a deserted island, would I complain of injustice if I build a house, and a strong wind blows it down? If I planted and grew a vegetable garden, and a deer came through and ate everything in one night, would I call it unfair? It’d suck and I’d do what I could to keep the deer out, but I probably wouldn’t accuse the deer of unfairness.

Then again, perhaps our struggle against nature, and animals, demolishing the fruits of our labor, really does come down to a sense of injustice: I worked to build the house, or plant the garden, or pick the fruits, it’s not right that someone/thing should take this.

A Starting Definition 
Maybe then justice is a state of affairs that allows us to enjoy the fruits of our labor. I think I’ll start with this as a basis for justice: Justice is a state of affairs that allows us to enjoy the fruits of our labors.

I may run into other concerns that force me to modify or hone this definition, but like most good working definitions, it’s simple enough to act as a principle towards which we would aim if we are trying to build justice in our society or community.

Justice and Sustainability 
There is another concern applicable even in a solitary individual situation: It would be possible to overutilize a particular material such that it negatively impacts the environment around you. Perhaps the individual in question strips the local environment of a certain food, which would have negative impacts not only for his own future, but that of the environment in which he lives.  

Justice is that state of affairs that allows the individual to enjoy the fruits of his labor, but that state would also include an obligation to maintain the environment he is a part of. Only in maintaining the environment he lives in, is he truly able to enjoy the fruits of his labor.  

Justice and Freedom 
In a community of people, the first condition of freedom is that it will need to be limited for each individual. When alone, individual freedom would not really be constrained. One could presumably take whatever material he could get to make whatever he could manage to make. But in a collection of humans, justice demanding that we be allowed to enjoy the fruits of our labors, taking materials or things that others have produced would be off limits to us.  

Justice and Equality
Justice would also probably require that all those in the community be given at least equal opportunity, but not certain if this would indeed be required. Would it be unfair for some people to start with more?  

If we are go establish a state of affairs in a community/society that allows each individual to enjoy the fruits of their labors, then it will require consideration of others, and based on that- equality and fairness in the application of the law, and at least as much as practically possible- equality in opportunities. 
It seems evident enough that at least equal opportunities ought to be legally provided for all individuals. I’m not sure if it is even possible to provide completely equal opportunities in practice, since individuals are born with different abilities and in different circumstances. In a preceding generation, there will be individuals that labor more ably, and with more natural gifts, than others. Even allowing that each member is enjoying the fruits of his labor, some members will enjoy more fruits than others. When those of the first group produce the subsequent generation, part of enjoying the fruits of their labors will include the ability to pass on what they want to their children. This will result in unequal starting points for those in the second generation.  

Should society make some sort of adjustment for those that have differing amounts? Our maxim (justice is that state of affairs that allows us to enjoy the fruits of our labors) doesn’t seem to require that we all start equally, only that we are allowed to enjoy the fruits of whatever labor we put in.  
In point of fact, requiring all to start equally would force those that earned more to forego enjoying the fruits of their labors with regard to the most important thing- their offspring. This type of societal adjustment would therefore violate the maxim.

That said, allowing a society to devolve through a few generations into haves and have nots is a well-trod path to discontent. Some kind of safeguard needs to be in place to disincentivize (or perhaps even prohibit) hoarding to the degree it approaches a kind of monopolization of resources.

Justice and Monopoly
Any community of humans will mean cooperation between the members, as well as competition. A fair competition will require at least fair rules and application among those competing.  

I think, that if we’re going to establish a state of affairs that allows the individuals in play to enjoy the fruits of their labor, then it would also be required to establish limits on monopolization. If one individual’s skill allows him, under the scope of “enjoying the fruits of his labor” to monopolize resources, then that monopolization effectively excludes others from enjoying the fruits of their own labor as well. An individual monopolizing resources within a community is therefore unjust in that the stated goal of justice can’t be realized by all members.

Justice and Public Goods
I should also consider that community works- those things that make the community function: legal system for resolving disputes, policing, public works for the furtherance of the communal good, will require taxes, which is a drain on the individual enjoyment of the fruits of his labor, but the fact of his living in society binds him together with the whole and both affords him rights, as well as places requirements on him. The fact that he has access to the benefits of society though mean he is, on that level, enjoying the fruits of communal labors he would have been unable to produce on his own.

Conclusion
It feels like the basic definition is a good starting point. Recognizing that unsustainable practices, monopolization and it’s near relative, hoarding, are consistent problems that need to be countered, doesn’t mean the principle is unworkable. In fact, the principle should be able to stand, and safeguards would need to be put in place to make sure that unsustainable practices and monopolization don’t demolish the state of affairs where each can enjoy the fruits of his labor. We also recognize that, in a community, limitations on personal freedoms through laws and taxes, are negative tradeoffs that contribute positively to the overall goal of providing a state of affairs that allow us to enjoy the fruits of our labors.

Of course, all these concepts exist on a spectrum. 100% taxes to contribute towards the public good is one end of the spectrum while no taxes as a principled stand for ‘the enjoyment of the fruits of individual labor is on the other. Where on the spectrum we should land in order to provide the optimum results towards the goal of allowing each to enjoy the fruits of his labor is the source of endless debate, and it’s in that area where the arguments will rage.  

Even so, I’m feeling more confident that the principle of justice I’ve settled on works for both individuals and communities.