Whether we are sorting out property disputes in North America, or working out whether two dioceses out of forty-four in England not agreeing to women bishops is worth bothering about, or live in Australia where (it seems to me) whatever is happening in Sydney is important to all other dioceses, or perhaps live in Uruguay which recently nominated a bishop the Province of the Southern Cone declined to confirm, the question "What is a diocese?" might be on our minds. It might also be useful to ask this question in the Diocese of Christchurch where we face overwhelming questions about the viability of many of our parish buildings, questions whose answers depend not only on the parishes themselves, but also on diocesan bodies such as Synod, Standing Committee and the Church Property Trustees (i.e. our diocesan trust board).
Sometimes we say in Anglican conversations that the basic ministry unit of Anglican churches is 'the diocese'. Theologically I understand this to mean that the key office(r) of the church is 'the bishop', so the church in its fullness is found where Christians gather in communion around their bishop. That is, the diocese is the church in its fullness, no smaller unit of ministry (on this theology) is the church in its fullness.
Clearly this is not all there is to say, because bishops do not arrive in a diocese solely by means of the diocese, which means that the notion that the diocese is the church in its fullness is up for discussion. That is, it is arguable that the diocese is not the church represented in its full fullness because a bishop is appointed to a diocese with the say so of other bishops (e.g. minimum of three to ordain a bishop), and, indeed, in some Anglican jurisdiction, with the say so of others (e.g. in ACANZP, a majority of the members of General Synod). Nevertheless, once a bishop is in place, a diocese stands alone if it desires: it can ordain its own clergy, train its own clergy. Well, maybe not all so simple: clergy implies regulations and over the years dioceses in our church and others have felt more secure having common regulations for ministry, to say nothing of common prayer books arrived at by more wisdom than resides in a diocese. Then there are arguments about the 'congregation' being the basic form of the church ...
Actually, cutting to the chase, I am doubtful (but open to arguments in comments) that the diocese is the basic ministry unit of the church. I suggest that in a Anglican framing of the church as an interdependent set of bodies, there is no one simple, discrete unit of the church. Rather there are units plural which in their complex relationships make up the church. There are parishes, but they can only operate so far without recourse to their diocese. There are dioceses, but they can only operate so far without recourse to the whole province/member church of the Communion to which they belong. There are provinces/member churches which can operate for a very long time and on a wide range of matters without recourse to the Communion, but recourse there is because something burns in the heart of the true church member which wants to be part of something larger. And the Communion itself keeps talking about re-union with Rome, Constantinople, and Geneva.
So, a diocese is not the church in its fullness. Bit of a negative answer to our question! What about a positive answer? I suggest, keeping the idea of interdependence in mind, that a diocese is both a corporation and a co-operative. It is a corporation in the sense that various bits of civil and ecclesial law talk about 'the Diocese of X' as a legal entity that can do this, own that, and even pass statutes and resolutions of its own. But it is also a co-operative in that 'the diocese' is hard to define without its bishop (elected as the local synod and (say) the General Synod co-operate), its synod and committees (which mostly do not exist without the co-operation of parishes as they come together to meet, to elect and to appoint), and its trust board(s) (whose members often are appointed by ... synod).
I haven't even talked about money, but here, also, the idea of corporation and co-operative are important. As a corporation a diocese owns property and receives monies, including bequests. As a co-operative a diocese finances aspects of its ministry and mission by contributions from its ministry units, those contributions ultimately being voluntary contributions in the sense that synod agrees to whatever system for collecting money is required to make things work (again, as synod agrees). The diocese which has large trust funds at its disposal is less dependent on the co-operation of synod for its workings than the diocese which has large dependency on parish contributions.
In ACANZP an often forgotten fact about diocesan life is that significant parts of what we do as 'dioceses' is dependent on a third source of funding, the annual grants from the St John's College Trust Board. I know of no episcopal unit in our church which could survive without immense pain and loss to its education and training if it suffered a sudden cessation of that funding. The good thing about that dependency is that it helps dioceses to meet together at General Synod and other forums because we go there to make sure that funding source is healthy and well governed. And don't let anyone else tell you otherwise.
What happens when a diocese gets to a point where it cannot sustain what it thinks of as being the essense of 'diocesan' life? We will watch the next 12 - 24 months of the life of the Diocese of Dunedin, the clergy of which have just received a sobering letter from its bishop, Kelvin Wright, about the pressing financial situation it faces.
Back to corporation and co-operative. I suggest a diocese is an entity within the ecclesial community of Anglicans which lives as both a corporation and a co-operative. Either/or is not an option.
Perhaps my question here, "What is a diocese?" is miscast. The better question might be, "Is a diocese what we think a diocese is?"