Secularism₁ is free thinking. Accordingly there is no way to define or distinguish the religious. Everything can be explicated, and can constitute a contribution to options and debates.  We generate Secularism₁  by explicating. In this space, there is no common doctrine, or belief system that anyone has to agree to in order to participate in the disagreement. Just the opposite: the possibility of a genuine disagreement means that there can be no such common belief system.  Historically, it was normalize in South Asia, until the beginning of Islamic conquests, which began around 900 CE. The British the used the Persian world “Hindu” to name this tradition, in contradistinction to Islam.