What is the Preamble to a Constitution for?

preamble.jpgFor various reasons, the question in the title has come up several times today. As a first thought, it seems to me that the Preamble to a Constitution sets out some general aspirational sentiments about the nature of the polity being created by that Constitution. It is a general statement which introduces the document and its purposes, ambitions, principles, and commitments, and thereby serves to explain its raison d’etre. In modern American parlance, it’s where the polity puts ‘the vision thing‘ for its members and others to find. Such broad brush strokes are inappropriate for binding text, but, because it is an expression of the polity’s vision, it is a useful aid for guiding the interpretation of the text which follows. Famously, the Preamble to the US Constitution does this in a single sentence. That to the Irish Constitution is a little longer.

So, my question is this: is the above paragraph a fair summary of what constitutional preambles do, or not?