Expenses in your business can be of various types (or for various purposes) – cost of goods sold, administrative and other operations related charges, payroll expenses, depreciation of assets etc. Those are the general types of expenses a business can have as a part of their income statement. They support the business in one way or another and are part of generating revenue at the end of the day. 

Question is however if all expenses are essentially also purchases? I would say “no, they aren’t”. The reason being, if you think about it, you’re buying goods and services, but there are some expenses, non-monetary ones for an example, which you aren’t buying no matter how you look at it. I do agree that you’re buying work from your employees, but you cannot buy depreciation.

A purchase is buying goods to be sold at a later date, buying materials used in everyday work or production, getting services needed to maintain the business (i.e. cleaning, internet, marketing etc.) – these are all expenses. A purchase is also buying an asset that you capitalize as part of your assets on the balance sheet and which you depreciate into expenses over its useful life. Purchase is buying the asset, but the expense charged over a longer period on the income statement isn’t a purchase anymore.

The reason I wanted to make this clarification is that purchases create payables (whether they are account payables, accruals or whatnot) whilst not all expenses do that. So do keep that in mind when exploring further into purchases and payables.