Tantrum?

In the past I have considered when does a child become a child - i.e. when do they move from simply a mass of cells into something with a consciousness?  I did not provide an answer, I am not sure there is one to be honest.

However, is there one for when a behavioural reaction becomes a tantrum?!  Friends of ours have ascribed their four week old screaming and kicking to a tantrum.  Emily and I do not think that's right.  One of the things that we have learnt since having Henry is that:

1)  You change your mind about everything you thought you would hold dear.
2)  Everybody, and I do mean everybody, has an opinion.  Be they friends, neighbours, passers-by, everybody think they know how it should be done.
3)  When you watch other people you think "ooo...I wouldn't have done that..."  In this, though see point 2 above!

But when does a tantrum become one?  We had a long chat about what the difference between a tantrum and a baby screaming was...we found it difficult to draw the line.  The issue is that they are both behavioural expressions of when something is wrong.  What we think the crux of the matter is, is the ability to access other strategies, such as talking about it, that are not available to a baby.  But it is far from decided in our household.