Take this thought experiment, which I found quite useful in making the distinction: you read a little about something, say postmodernism, and then shut yourself in a room for a bit. You have a pen and a lot of paper, and you sit down and write out your idea of what postmodernism is. You read what you've written. You think it doesn't look right, so you edit it and write an improvement. You reread it, edit it, and so on.....

Well....we actually have a perfect example of this in the contradictory texts of the four Gospels. Effectively, different drafts of a religion still survive. Yet a person does not call themselves a Luke-ian, or a Matthew-ian.......they call themselves a Christian.

The fact that there are probably as many different takes on Christianity as there are people who believe in it, does not alter our ability to identify a meme called 'Christianity'. So I would suggest that the core feature of a meme is it's ability to be reduced to a simple label......to the extent that in extreme cases the meme may actually be no more than the label.

Thus the meme is not the full extent of that which actually exists in the head of the 'holder' of it, but is solely that element that enables anyone else to identify that there is actually a meme there. The 'identifier' component is the actual meme.

So in other words, commonality of an idea may spread thoughout society, but the meme is not the actual full package of the idea, but only the ability to 'recognise' that commonality......i.e the point at which a label is atached.

Two people may intrinsically hold the exact same core idea, but unless they or society can actually identify that commonality through the public expression and perception of it......it's hard to see in what sense a meme exists. Thus a meme is not something that is intrinsic to the holder and exists as an entity in its own right.....but to all extents and purposes is the perception of commonality.....whether that perception is true or not.

That's my take. The "ah, thats the same thing I believe in" is the actual meme and what is propagated.........regardless of whether the idea is actually the same.

Thus one could identify a meme as being that component that makes a person think that they hold the same idea as someone else, rather than the actual idea itself.