The philosophy of happiness is the philosophical concern with the existence, nature, and attainment of happiness. Some philosophers believe happiness can be understood as the moral goal of life or as an aspect of chance; indeed, in most European languages the term happiness is synonymous with luck. Thus, philosophers usually explicate on happiness as either a state of mind, or a life that goes well for the person leading it. Given the pragmatic concern for the attainment of happiness, research in psychology has guided many modern-day philosophers in developing their theories. Ancient Greece Democritus Democritus (c. 460 – c. 370 BC) is known as the 'laughing philosopher' because of his emphasis on the value of 'cheerfulness'. Plato Plato (c. 428 – c. 347 BCE) teaches in the Republic that a life committed to knowledge and virtue will result in happiness and self-realization. To achieve happiness, one should become immune to changes in the material world and strive to gain the knowledge of the eternal, immutable...