Atheism is the denial of a god or gods, in theory or in practice. As such it has frequently been used as an accusation against ideological opponents on a point of definition. It may also be used to describe amoral behaviour. Atheism in its ultimate forms denies a spiritual aspect to man. With the discovery of scientific explanations for phenomena and with increasing materialism, disenchantment with former religious explanations has given rise to atheism among wide range of people who would debate the existence of a god as a hypothesis. This might include agnostics or adherents of nontheistic faiths such as Marxism.
[Catholicism] The word atheism is applied to phenomena which are quite distinct from one another. For while God is expressly denied by some, others believe that man can assert absolutely nothing about Him. Still others use such a method to scrutinize the question of God as to make it seem devoid of meaning. Many, unduly transgressing the limits of the positive sciences, contend that everything can be explained by this kind of scientific reasoning alone, or by contrast, they altogether disallow that there is any absolute truth. Some laud man so extravagantly that their faith in God lapses into a kind of anaemia, though they seem more inclined to affirm man than to deny God. Again some form for themselves such a fallacious idea of God that when they repudiate this figment they are by no means rejecting the God of the Gospel. Some never get to the point of raising questions about God, since they seem to experience no religious stirrings nor do they see why they should trouble themselves about religion. Moreover, atheism results not rarely from a violent protest against the evil in this world, or from the absolute character with which certain human values are unduly invested, and which thereby already accords them the stature of God. Modern civilization itself often complicates the approach to God not for any essential reason but because it is so heavily engrossed in earthly affairs.
Undeniably, those who willfully shut out God from their hearts and try to dodge religious questions are not following the dictates of their consciences, and hence are not free of blame; yet believers themselves frequently bear some responsibility for this situation. For, taken as a whole, atheism is not a spontaneous development but stems from a variety of causes, including a critical reaction against religious beliefs, and in some places against the Christian religion in particular. Hence believers can have more than a little to do with the birth of atheism. To the extent that they neglect their own training in the faith, or teach erroneous doctrine, or are deficient in their religious, moral or social life, they must be said to conceal rather than reveal the authentic face of God and religion.
Modern atheism often takes on a systematic expression which, in addition to other causes, stretches the desire for human independence to such a point that it poses difficulties against any kind of dependence on God. Those who profess atheism of this sort maintain that it gives man freedom to be an end unto himself, the sole artisan and creator of his own history. They claim that this freedom cannot be reconciled with the affirmation of a Lord Who is author and purpose of all things, or at least that this freedom makes such an affirmation altogether superfluous. Favouring this doctrine can be the sense of power which modern technical progress generates in man. Not to be overlooked among the forms of modern atheism is that which anticipates the liberation of man especially through his economic and social emancipation. This form argues that by its nature religion thwarts this liberation by arousing man's hope for a deceptive future life, thereby diverting him from the constructing of the earthly city. Consequently when the proponents of this doctrine gain governmental power they vigorously fight against religion, and promote atheism by using, especially in the education of youth, those means of pressure which public power has at its disposal. (Second Vatican Council. Gaudium et Spes, 1965).
Occasionally statistics from polls concerning religious beliefs are published. For example, one poll in Sweden credits 48% of the population with belief in God, and then reports that 5% of the population regularly attend church. Atheism is sometimes imputed to the ordained religious who leave their ministries, orders or churches; but it may more frequently be represented by inadequately educated and theologically prepared clergy who have no deep comprehension of their faith and in an attempt at modernism, reduce their God to a humanistic value.
The Jews and early Christians were accused of atheism by the Romans because they refused to recognize the Roman gods and the Emperor as divinities. Orthodox Christians used the accusation against various heretics, notably those who acknowledged God but denied the Trinity.