What’s the difference between Nationalism and Republicanism?

Spent the morning in Dublin today, and in the course of conversations there someone brought the distinctions that might be made between Republicanism and Nationalism. The latter is almost extinct in the Republic these days. The former, perhaps rather self consciously, the epithet of choice of Fianna Fáil.

It set me thinking as to what northern Irish voters are actually being offered, and how well our descriptions fit what’s actually on offer? Here for instance, courtesy of Belfast Unicorn, is a fascinating clipping from George Orwell (who it must be admitted had it in for nationalism):

A nationalist is one who thinks solely, or mainly, in terms of competitive prestige. He may be a positive or a negative nationalist — that is, he may use his mental energy either in boosting or in denigrating — but at any rate his thoughts always turn on victories, defeats, triumphs and humiliations.

He sees history, especially contemporary history, as the endless rise and decline of great power units, and every event that happens seems to him a demonstration that his own side is on the upgrade and some hated rival is on the downgrade.

But finally, it is important not to confuse nationalism with mere worship of success. The nationalist does not go on the principle of simply ganging up with the strongest side. On the contrary, having picked his side, he persuades himself that it is the strongest, and is able to stick to his belief even when the facts are overwhelmingly against him.

Nationalism is power-hunger tempered by self-deception. Every nationalist is capable of the most flagrant dishonesty, but he is also — since he is conscious of serving something bigger than himself — unshakeably certain of being in the right.” George Orwell, Notes on Nationalism, 1945.

All very fine. My quibble though is that the apparent assumption that only unionism affords a detached antidote to such unreconstructed tribal marking. Or that indeed, through it’s long attachment to a liberal English state that Unionism’s baser nationalist impulses are expurgated from the overall ‘offering’.

Yet on the ‘nationalist’ side, the elision between the term is so ubiquitous that they are effortlessly interchangeable. My question to you is, is there a difference? If not why not? And if yes, what are the mainline divergences?