One problem I have enjoyed all my life is the inability to understand fancy theories. My brain can only understand simple things, so I like to go back to principle in everything and, once I have identified the principle to my satisfaction, I know the foundations to which Rococo details can be added.
So, what about this Brexit thing? In order to know what leaving the European Union means it seems pretty obvious to me that it is necessary to identify what the EU is. Once that is defined, we know what the people voted to extricate the country from and can reach a principled view of what the government must do.
So, what is the EU?
The answer must be that it is the legal framework that locks the member states of the EU together. It is not the institutions of the EU (such as the Commission, Council of Ministers, European Parliament and Court of so-called Justice), nor is it the people who work within those institutions. The UK is only involved in those institutions because it is legally obliged to be involved through its agreement to various treaties that require us to be involved.
Everything else flows from that, including various aspects of the EU that are administrative rather than institutional. We are signed-up to the Common Agricultural Policy, the Common Fisheries Policy, the single market, the customs union and various other arrangements that are set-up by the EU institutions by virtue of being party to treaties that establish the institutions. We are not involved in the CAP and the CFP voluntarily but because it is a necessity as result of the effect of the treaties to which we are a party. Importantly we are not in the CAP and such by virtue of a stand-alone treaty, we are in it because we are a party to treaties setting-up the EU institutions.
I was thinking of writing a piece citing the relevant treaties and analysing their major provisions, but I cannot be bothered because principle is principle and stands by itself without citation of authority. We can only leave the EU by no longer being bound by the the treaties. Necessarily that means we are no longer members of the EU institutions. It also means we are no longer bound by any policies of the EU that are not already incorporated into law in this country. Many EU policies are part of law in the constituent countries of the UK by virtue of domestic legislation but many are not. For example, CAP, CFP, single market and customs union bind us by virtue of EU policy not by virtue of domestic law in the UK - they bind us because we are members of the EU but our parliaments and assemblies have not adopted them as part of domestic law.
That is not to say there is nothing to negotiate. As a result of our membership of the EU, the EU has undertaken obligations to various citizens of the UK. Former MEPs, Commissioners and civil servants are entitled to EU pensions. We cannot just wash our hands, no matter how tempting it might be, and claim to have no on-going obligation to contribute to those pensions. In fact it goes much wider than that, the EU has entered into numerous contracts with individuals and companies which will have consequences for many years to come, it has also entered into agreements with artistic and sporting groups, NGOs and non-EU countries that involve an obligation to make payments for years to come. We were members when those arrangements were made and cannot wash our hands of the obligation to continue to make contributions in this field as well. That is what "terms of exit" are all about.
Matters such as our future trading arrangement with people and businesses within countries that will remain members of the EU are nothing to do with leaving the EU. They are about what happens after we have left. There is, for example, no question of remaining a "member" of the single market. Our government might, if it is so minded, negotiate an arrangement under which the UK has exactly the same trading access to EU countries as it has currently, but that is a post-Brexit arrangement not a term of leaving the EU.
Mrs May, who remains something of an enigma to me because I cannot recall ever hearing her expound her personal political philosophy, has said many times "Brexit means Brexit". I hope she stands by her words and makes clear there is no such thing as "hard" or "soft" Brexit. Brexit means withdrawing from the treaties. No more, no less. Everything else is an arrangement of the position once we have exited.