Me!? Expelled from the Conservative Party, J!? If only you knew how funnny that is...
I've just consulted the Bloomsbury Dictionary, Chambers, TOED, the Encyclop�dia Britannica, Hutchinson's Encyclopedia and Collier's Encyclopedia (USA)...all to hand...and not one of them credits either Oceania or Australasia with being a continent. They all employ vague words/phrases such as...(quote) "regions, lands, divisions, groups, collective name, colloquially known as, vaguely defined"...and so forth.
Re Australasia - a name invented by the French in the 1750s - TOED says it is: "used to include Australia and its adjoining islands". Re Oceania - a name invented by the French in the 1840s - the OED says: it is "a general name for the islands of the Pacific and its adjacent seas". In neither case, does the word �continent' appear in the definition. Nor did either of the Frenchmen concerned believe he was naming a continent. (One thing you can say for sure about 18th century scientists is that they knew their Latin!)
In answer to JustSia's query on Europe and Asia...my apologies for overlooking it earlier... these were named by the ancient Greeks, so of course history comes into the matter as well as geography. Bear in mind that the ancient Greeks' knowledge of geography was necessarily somewhat circumscribed!
Incidentally, I didn't claim that all contiguous lumps of the earth were continents...what I did claim was that - in order to be a continent - any given lump of earth had to be contiguous. Not at all the same thing...and certainly inapplicable to a myriad of islands.
As far as I am concerned, one can call Australasia and Oceania �geographical regions', call them �archipelagoes', call them whatever one likes...but one really cannot call them �continents'.
And there, I for one shall leave things. Cheers to all.