Liberalism developed from the political writings of John Locke in the 17th century advocating for natural rights and the economic writings of Adam Smith in the 18th century supporting free markets. Key concepts of liberalism include freedom, equality, and toleration. There are three strands of liberalism - classical emphasizing individual liberty and limited government, progressive supporting state welfare and equality of opportunity, and neo-liberal rejecting progressive views and refocusing on individual needs. Current liberal thinking combines classical and progressive views supporting individual freedom, equality of opportunity, social justice, and protection of individual rights.