Science progresses because of advancement in theories. Dictionary definitions show that the word theory can take on many meanings, including “a mental view” or “contemplation,” “a concept or mental scheme of something to be done, or the method of doing it; a systematic statement of rules or principles to be followed,” a “system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment and is propounded or accepted as accounting for the known facts; statements of what are held to be the general laws, principles, or causes of something known or observed,” a “mere hypothesis, speculation, conjecture” (Gregor 2006).