Implicit atheism and explicit atheism are subcategories of atheism

Atheism

Atheism is, in a broad sense, the rejection of belief in the existence of deities. In a narrower sense, atheism is specifically the position that there are no deities...

 coined by George H. Smith

George H. Smith

George Hamilton Smith is an American author, editor, educator and speaker.-Biography:Smith grew up mostly in Tucson, Arizona, and attended the University of Arizona for several years before leaving without a degree; he relocated to Los Angeles during 1971. With the help of libertarian editor Roy A...

 (1979, p.13-18). Implicit atheism is defined by Smith as "the absence of theistic belief without a conscious rejection of it". Explicit atheism is defined as "the absence of theistic belief due to a conscious rejection of it".
Explicit atheists have considered the idea of deities and have rejected belief that any exist. Implicit atheists thus either have not given the idea of deities much consideration, or, though they do not believe, have not rejected belief.

Implicit atheism

Smith defines implicit atheism as "the absence of theistic belief without a conscious rejection of it". "Absence of theistic belief" encompasses all forms of non-belief in deities. This would categorize as implicit atheists those adults who have never heard of the concept of deities, and those adults who have not given the idea any real consideration. Also included are agnostics who assert they do not believe in any deities (even if they claim not to be atheists). Children are also included, though, depending on the author, it may or may not also include newborn babies. As far back as 1772, Baron d'Holbach

Baron d'Holbach

Paul-Henri Thiry, Baron d'Holbach was a French-German author, philosopher, encyclopedist and a prominent figure in the French Enlightenment. He was born Paul Heinrich Dietrich in Edesheim, near Landau in the Rhenish Palatinate, but lived and worked mainly in Paris, where he kept a salon...

 said that "All children are born Atheists; they have no idea of God."
Smith is silent on newborn children, but clearly identifies as atheists some children who are unaware of any concept of any deity.
Ernest Nagel

Ernest Nagel

Ernest Nagel was a Czech-American philosopher of science. Along with Rudolf Carnap, Hans Reichenbach, and Carl Hempel, he is sometimes seen as one of the major figures of the logical positivist movement....

 contradicts Smith's definition of atheism as merely "absence of theism", acknowledging only explicit atheism as true "atheism".

Explicit atheism

Smith observes that some motivations for explicit atheism are rational and some not. Of the rational motivations, he says:
For Smith, explicit atheism is subdivided further into three groups:

• a) the view usually expressed by the statement "I do not believe in the existence of a god or supernatural being";
• b) the view usually expressed by the statement "God does not exist" or "the existence of God is impossible"; and
• c) the view which "refuses to discuss the existence of a god" because "the concept of a god is unintelligible" (p.17).

Although, as mentioned above, Nagel opposes identifying what Smith calls "implicit atheism" as atheism, the two authors do very much agree on the three-part subdivision of "explicit atheism" above, though Nagel does not use the term "explicit".

Other typologies of atheism

The difference between Nagel on the one hand and d'Holbach

Baron d'Holbach

Paul-Henri Thiry, Baron d'Holbach was a French-German author, philosopher, encyclopedist and a prominent figure in the French Enlightenment. He was born Paul Heinrich Dietrich in Edesheim, near Landau in the Rhenish Palatinate, but lived and worked mainly in Paris, where he kept a salon...

 and Smith on the other has been attributed to the different concerns of professional philosophers and layman proponents of atheism (see Smith (1990, Chapter 3, p.51-60), for example, but also alluded to by others).

Everitt (2004) makes the point that professional philosophers are more interested in the grounds for giving or withholding assent to propositions:

We need to distinguish between a biographical or sociological enquiry into why some people have believed or disbelieved in God, and an epistemological enquiry into whether there are any good reasons for either belief or unbelief... We are interested in the question of what good reasons there are for or against God's existence, and no light is thrown on that question by discovering people who hold their beliefs without having good reasons for them. (p.10)

So, in philosophy (Flew and Martin notwithstanding), atheism is commonly defined along the lines of "rejection of theistic belief". This is often misunderstood to mean only the view that there is no God, but it is conventional to distinguish between two or three main sub-types of atheism in this sense. However, writers differ in their characterization of this distinction, and in the labels they use for these positions.

The terms weak atheism and strong atheism (or negative atheism and positive atheism) are often used as synonyms of Smith's less-well-known implicit and explicit categories. However, the original and technical meanings of implicit and explicit atheism are quite different and distinct from weak and strong atheism. "Strong explicit" atheists assert that it is false that any deities exist. "Weak explicit" atheists assert they do not believe in deities, but do not assert it is true that deities do not exist. Those who do not believe any deities exist, but do not assert their non-belief are included among implicit atheists. Among weak implicit atheists are thus sometimes included the following: children and adults who have never heard of deities; people who have heard of deities but have never given the idea any considerable thought; and those agnostics who suspend belief about deities, but do not reject such belief.

People who do not use the broad definition of atheism as "absence of theism", but instead use the most common definition "disbelief in or denial of the existence of God or gods", would not recognize mere absence of belief in deities (implicit atheism) as a type of atheism at all, and would tend to use other terms, such as "skeptic

Skepticism

Skepticism has many definitions, but generally refers to any questioning attitude towards knowledge, facts, or opinions/beliefs stated as facts, or doubt regarding claims that are taken for granted elsewhere...

" or "agnostic

Agnosticism

Agnosticism is the view that the truth value of certain claims—especially claims about the existence or non-existence of any deity, but also other religious and metaphysical claims—is unknown or unknowable....

", or even the heavy-handed "non-atheistic non-theism", for this position.

See also

• Non-theism
• Strong and weak atheism
• Ignosticism
  Ignosticism
  Ignosticism or igtheism is the theological position that every other theological position assumes too much about the concept of God and many other theological concepts...
  
  
• Agnosticism
  Agnosticism
  Agnosticism is the view that the truth value of certain claims—especially claims about the existence or non-existence of any deity, but also other religious and metaphysical claims—is unknown or unknowable....