In economics, one of the most important concepts is 'opportunity cost' - the idea that once you spend your money on something, you can't spend it again on something else.

Governments enjoying surpluses have a very strong temptation to splash money around, and while tax cuts are always appealing, cutting taxes at the top of a boom runs the real risk of creating a structural deficit when the boom subsides.

Let us be honest with each other. The threat to marriage is not the gays. It is a lack of loving commitment - whether it is found in the form of neglect, indifference, cruelty or adultery, to name just a few manifestations of the loveless desert in which too many marriages come to grief.

Nobody looks at opinion polls with more attention than politicians, but of course you've got to remember that a single poll is a snapshot in time.

While our energy efficiency is improving, there is a very high correlation, almost near perfect correlation, between GDP growth, and energy usage.

I am an ambitious person, but I am not ambitious in the sense that I want jobs only for the sake of them... I am here to do things I think are worthwhile. I am always careful that the political positions I take are consistent with good policy. I would not want to be prime minister of Australia at any price.

I've always been prepared to put my money where my mouth is.