 In the western tradition, there have been a few periods of especially active discussion of these prolegomenal issues. The Neo-Platonic era was one (see the discussion of negative theology in the entry on  Plotinus),  the high medieval period (1100–1400 or so) was another, the Enlightenment movement in 17th–18th century Europe (especially the empiricist portion of it) was a third. More recent discussions have involved both analytic and continental figures: A.J. Ayer, Ludwig Wittgenstein, Martin Heidegger, Antony Flew, Norman Malcolm, Emmanuel Levinas, and William P. Alston have each discussed, in very different ways, the question of whether and how our language might succeed in referring to transcendent entities. However, since the 1970s, analytic philosophers have turned away from a focus on language to a revival of metaphysics, and the “problem of religious language” has been much less prominent.