Wittgenstein, AJ Ayer, The Vienna Circle, John Hick, a Celestial City, and whether or not that's a duck, or a rabbit...

https://i2.wp.com/www.learningspy.co.uk/wp-content/uploads/2016/06/duck-rabbit.jpg 

Open the image at the link above and have it handy for when you're asked to look at the Duck-Rabbit, please. :-)