Implicit and explicit atheism
Implicit atheism and explicit atheism are subsets of atheism coined by George H. Smith (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 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.
The man who is unacquainted with theism is an atheist because he does not believe in a god. This category would also include the child with the conceptual capacity to grasp the issues involved, but who is still unaware of those issues. The fact that this child does not believe in god qualifies him as an atheist.
Ernest Nagel contradicts Smith's definition of atheism as merely "absence of theism", acknowledging only explicit atheism as true "atheism".
I shall understand by "atheism" a critique and a denial of the major claims of all varieties of theism... atheism is not to be identified with sheer unbelief... Thus, a child who has received no religious instruction and has never heard about God, is not an atheist – for he is not denying any theistic claims. Similarly in the case of an adult who, if he has withdrawn from the faith of his father without reflection or because of frank indifference to any theological issue, is also not an atheist – for such an adult is not challenging theism and not professing any views on the subject.
Explicit atheism 
Smith observes that some motivations for explicit atheism are rational and some not. Of the rational motivations, he says:
The most significant variety of atheism is explicit atheism of a philosophical nature. This atheism contends that the belief in god is irrational and should therefore be rejected. Since this version of explicit atheism rests on a criticism of theistic beliefs, it is best described as critical atheism.
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 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" or "agnostic", or even the heavy-handed "non-atheistic non-theism", for this position.
See also 
- Smith, George H. (1979). Atheism: The Case Against God. Buffalo, New York: Prometheus. pp. 13–18. ISBN 0-87975-124-X.
- d'Holbach, P. H. T. (1772). Good Sense. Retrieved 2010-05-12.
- Nagel, Ernest (1959). "Philosophical Concepts of Atheism". Basic Beliefs: The Religious Philosophies of Mankind. Sheridan House.
reprinted in Critiques of God, edited by Peter A. Angeles, Prometheus Books, 1997.
- Smith, George H. (1990). Atheism, Ayn Rand, and Other Heresies. pp. 51–60.
- Everitt, Nicholas (2004). The Non-existence of God: An Introduction. London: Routledge. ISBN 0-415-30107-6.
- "Dictionary.com/atheism". Retrieved 2006-03-05.