I believe that the common good is the construction of a society of equality and safety that holds a place for all people within it. This society does not discriminate against those who have different capabilities or interests. Instead, it tries to create a place for all people who are invested in the good of all others. The good of all others means their safety, well-being, and personal fulfillment. The difficult of constructing a concept of the common good is that everyone has a slightly different conception of what is good. However, as long as each person in the society can agree that each person has the inherent right to pursue what he or she believes to be good under the auspices of not harming anyone else or him or herself, and actively work to make the society safe and fruitful, then the efforts of the vast majority of people will be good and indeed work to better the society. While some efforts may be misguided, these will be relatively few and hardly matter in the long run.
For example, some people are interested in the body and its workings. These people will naturally be guided to working in medicine and health. Of course, everyone is interested in keeping their body healthy and problem-free, so naturally this service will be valued in society. Others are fascinated with the study of history. Knowing the history of a civilization is both useful and interesting to people. My providing equal opportunity to everyone who can show that he or she has good intentions and is invested in working, every person will have a function and the necessary resources to fulfill that interest or service. Some people will be interested in growing food or farming animals, others in transporting goods, and others in governing and helping others. The roles that people naturally gravitate to will properly distribute to the roles are that are needed.
While some may say that the common good should not be pursued because it can never completely be achieved, I do not believe that is a reason to not try to pursue it regardless. The rampant injustice in the world convinces me that even if the common good is never completely achieved or perfectly sought, it is still worth striving toward. Extreme economic disparity, poverty, disease, prejudice, illness, and war are all proof that as a global community, we should seek out a common goal that puts aside these differences and looks forward to something that everyone can rejoice in.
Though everyone would have the option to participate in the common good, some people would likely need to be excluded. Anyone who could not commit to working to achieve the common good would need to be evaluated. Of course, some people would simply be incapable of participating. This might include people who are mentally or physically challenged and require rehabilitative services. These people will be helped and hopefully rehabilitated. If provided proper resources, many of these people could still be useful to society and allowed to pursue their interests in a constructive way that complements their capabilities. For those who could not commit or refrain from violence, another system would have to be put in place to house or help them.
Though this ideal is far from the current state of the world, I do not believe that it is entirely impossible. If people truly believed in the common good and were willing to humble themselves for it, then it could work. This would mean that the wealthy would need to give up their excessive wealth. It would mean that the lazy would need to make a plan and commit to working. It would mean that those with prejudices would need to drop them. While highly improbable, it does not seem impossible.