Taxation has only been mentioned in passing, but, as most people are only too well aware, it plays a very important and prominent role in modern life, to the extent that income is frequently very much reduced after tax liabilities have been met. Almost all income is assessable for tax purposes, although, depending upon personal circumstances and the detailed provisions of particular tax systems, taxpayers may get various allowances and expenses against their income to reduce their liability. In the United Kingdom, earnings from certain sources, such as National Savings Certificates, are not taxed, while some earnings, such as interest earned on building society accounts, have been paid net of tax. The general rule, however, is that most income is taxable, and because there is often a wide discrepancy between earnings gross of tax and the same earnings net of tax, the majority of people are more interested in knowing the size of the latter. Wage-earners look at the last figure on their pay-slips to discover what is left for them to spend after the "taxman" has had "his share", and the majority of investors will also be principally interested in knowing what is left for them at the end of the day.