Simplicity is the state or quality of being simple. Something easy to understand or explain seems simple, in contrast to something complicated. Alternatively, as Herbert A. Simon suggests, something is simple or complex depending on the way we choose to describe it. In some uses, the label "simplicity" can imply beauty, purity, or clarity. In other cases, the term may suggest a lack of nuance or complexity relative to what is required.
The concept of simplicity is related to the field of epistemology and philosophy of science (e.g., in Occam's razor). Religions also reflect on simplicity with concepts such as divine simplicity. In human lifestyles, simplicity can denote freedom from excessive possessions or distractions, such as having a simple living style.
In some contextual uses, "simplicity" can imply beauty, purity, or clarity. In other cases, the term may have negative connotations, as when referring to people as simpletons.
Simplicity is the greatest form of sophistication, to think simply is to understand the benefit of a simpler approach first. Like Sherlock Holmes "the simplest explanation is often the most plausible". When confronting a crime scene at face value. 
The concept of simplicity has been related to in[clarification needed] the field of epistemology[clarification needed] and philosophy of science.[clarification needed]
According to Occam's razor, all other things being equal, the simplest theory is most likely true. In other words, simplicity is a meta-scientific criterion by which scientists evaluate competing theories.
A distinction is often made by many persons.[by whom?] between two senses of simplicity: syntactic simplicity (the number and complexity of hypotheses), and ontological simplicity (the number and complexity of things postulated). These two aspects of simplicity are often referred to as elegance and parsimony respectively.
John von Neumann defines simplicity as an important esthetic criterion of scientific models:
[...] (scientific model) must satisfy certain esthetic criteria - that is, in relation to how much it describes, it must be rather simple. I think it is worth while insisting on these vague terms - for instance, on the use of word rather. One cannot tell exactly how "simple" simple is. [...] Simplicity is largely a matter of historical background, of previous conditioning, of antecedents, of customary procedures, and it is very much a function of what is explained by it.
Simplicity is a theme in the Christian religion. According to St. Thomas Aquinas, God is infinitely simple. The Roman Catholic and Anglican religious orders of Franciscans also strive for personal simplicity. Members of the Religious Society of Friends (Quakers) practice the Testimony of Simplicity, which involves simplifying one's life to focus on what is important and disregard or avoid what is least important. Simplicity is tenet of Anabaptistism, and some Anabaptist groups like the Bruderhof, make an effort to live simply.
Main article: Simple living
In the context of human lifestyle, simplicity can denote freedom from excessive material consumption and psychological distractions.
A distinction is often made between two fundamentally distinct senses of simplicity: syntactic simplicity (roughly, the number and complexity of hypotheses), and ontological simplicity (roughly, the number and complexity of things postulated). [...] These two facets of simplicity are often referred to as elegance and parsimony respectively. [...] The terms ‘parsimony’ and ‘simplicity’ are used virtually interchangeably in much of the philosophical literature.