to even. How a society considers what is secular may also change, where nominally spiritual beliefs become part of public or private life without being recognised as religious. As secularists are a minority in most communities, secularism is often stigmatised. Proponents of religious society challenge secular society on the basis of morality, saying that secularism lacks a meaningful way to incentivise moral behaviour among its members. Secular philosophy Secularism is considered in political philosophy and philosophy of religion. As a philosophy, secularism is closely associated with naturalism and materialism, rejecting consideration of immaterial or supernatural substances, such as a soul, in favour of a material universe. This secular materialism and rationalism forms the basis of most modern empirical science. During the Age of Enlightenment, liberal European philosophers such as Baruch Spinoza, John Locke, Montesquieu, Voltaire, David Hume, Adam Smith, and Jean-Jacques Rousseau all proposed various forms of separation of church and state. The work of well known moral philosophers such as Derek Parfit and Peter Singer, and even the whole field of contemporary bioethics, have been described as explicitly secular or non-religious. A major issue considered by secular philosophy is the nature of morality in a material universe. Secular ethics and secular morality describe systems of right and wrong that do not depend on religious or supernatural concepts. Much of the philosophy of Friedrich Nietzsche is developed in response to this issue. Under secular ethics, good is typically defined as that which contributes to "human flourishing and justice" rather than an abstract or idealised conception of good. Secular ethics are often considered within the frame of humanism. Secularism in late 20th century political philosophy It can be seen by many of the organisations (NGOs) for secularism that they prefer to define secularism as the common ground for all life stance groups, religious or atheistic, to thrive in a society that honours freedom of speech and conscience. An example of that is the National Secular Society in the UK. This is a common understanding of what secularism stands for among many of its activists throughout the world. However, many scholars of Christianity and conservative politicians seem to interpret secularism more often than not, as an antithesis of religion and an attempt to push religion out of society and replace it with atheism or a void of values, nihilism. This dual aspect (as noted above in "Secular ethics") has created difficulties in