From the perspective of faculty, shared governance ought to serve the faculty in shaping and recommending policy to the administration. Many statements about shared governance emphasize this by saying that the administration should follow policy recommendations duly approved by academic senates, and give compelling reasons when they do not.
Why should faculty have this authority? One answer, with a long tradition, is that faculty are experts in their fields, and therefore have the legitimate claim over directing the academic policies of their institutions. This is a claim about professional knowledge, judgment, and status, and is a common feature of every profession's assertion of self-regulatory authority. Since only medical doctors can make knowledgeable judgments of the work of medical doctors, medical doctors should have that authority; since only chemists can determine whether chemists are doing their work properly, chemists should regulate their own work.
Over the last 40 years or so, this authority has eroded, for every profession, as corporatization, privatization, and bureaucratization have taken over in formerly public-serving fields. Shared governance is a slow process; predatory capitalism can't abide this.
The question is, what would make it seem reasonable to deny that doctors should have the authority and responsibility to determine what doctors should do? Why on earth would the regulation of doctors fall to people with financial spreadsheets? Similarly, why would the determination of academic policy fall to such people, many of whom are absolutely unable to talk about academic policy in any terms other than cash?
I am certain this is partly the result of the delegitimation of claims to expert knowledge. The authority of doctors, chemists, philosophers, or anyone else have become suspect. Expertise is now the function of computer programs, and the reduction of all values to money is an unquestionable ideology.
Under those real conditions, what could legitimate shared governance? My answer comes from the underclass of the academic profession, the permanently temporary, "contingent," or, as I prefer, the tenuous-track faculty. This super-majority of faculty (more than 75% of all college and university faculty) have been excluded from shared governance all along, and are only now getting some voice.
1. Labor. Tenuous-track faculty do the majority -- the vast majority -- of teaching work; therefore, tenuous-track faculty deserve a share in governance. The principle of justice here is a kind of proportionality: those who do most work have most at stake.
2. Civil and human rights. Tenuous-track faculty are people, actual real human beings, and as people deserve a share in governance. This is a liberal-democratic claim, that individual human beings have the right to self-determination and participation in social institutions.
3. Expertise. And by the way, yes, we are experts, thank you. We may lack full credentials in some cases, and we lack privilege and prestige, but we still have expert knowledge. There is a subtext to this: if shared governance is denied to those who do the work that recognized experts do, then the institutional power of recognized experts looks much more like mere privilege.
* Allegedly because of "competition," but of course the real reason all institutional change has to be rapid and dramatic is to perpetuate crisis, stun people, and create opportunities for seizing still more power).
§ I don't think it's an accident that this comes when shared governance is losing clout.