The principle that requires a company to match expenses with related revenues in order to report a company's profitability during a specified time interval. Ideally, the matching is based on a cause and effect relationship: sales causes the cost of goods sold expense and the sales commissions expense. If no cause and effect relationship exists, accountants will show an expense in the accounting period when a cost is used up or has expired. Lastly, if a cost cannot be linked to revenues or to an accounting period, the expense will be recorded immediately. An example of this is Advertising Expense and Research and Development Expense.