Why are the potentials the same?

[s3a]

Could someone tell me why the potentials are the same in http://i.imgur.com/EdnqE.jpg.

I am talking about right under the part where it says "Also, the potentials across them are now the same, so that V = q/C gives". I understand everything prior to that. I even understand the stuff after it! I just need to justify to myself the theory behind why the potentials are equal so that I can move on. Please be elaborate but a short response is fine.

Any input would be greatly appreciated!
Thanks in advance!

 

[rock.freak667]

They are connected in parallel so the potential is the same for both.

 

[s3a]

How do you discern that they are parallel? I was under the impression that "(b) After" is in series.

 

[rock.freak667]

The positive terminal is connected to the positive terminal in both capacitors.