Why can't I see any transparency on my material with Eevee? This feels like such a basic question, but I can't work it out.  I need to render a semi transparent Lego block and see the back faces of the block.  



I'm using Eevee in Blender 2.8 and have created a Principled BDSF texture with a mix shader and a Transparent BDSF.  I'm passing an RGB node with black colour (I tried white too) into the Transparency BDSF. I am seeing transparency, but I can't see the back faces and cant find an option for 2 sided material or mesh in this version of blender.



How do I do this please?
First of all with Principled BSDF you don't have to mix it with Transparent because it already has its own transparency mixer, Alpha slider. The second - in material tab in settings make sure your Blend mode is 'Alpha Blend' and 'Show Backface' is enabled.

UPD. 'Show Backface' option indeed shows the back sides of the polygons but simultaneously stops to show the front sides. I guess in some cases it can be used as a kind of fake semi-transparency, but in fact it is not.