What is importance of Philosophy, Psychology, and Political Science in management?

Wow, what a question!

These things are hugely important in life.  In management, you have power, so that makes them even more important. 

Philosophy - Business ethics is a branch of philosophy.  Get your ethics wrong, and your business will cease to exist.

Political science - Everything is political, but a good example of where business, political science and philosophy might meet is the area of government regulation.  Is it right for the government to regulate this particular thing?  And if so, what is the right way to do it?  Does practicality trump principle?  In whose interest should the regulation work most?

Psychology - On a day to day basis, this is the one that is most closely relevant to management.  That salesperson seems to be making fewer calls today ... I wonder why?

i fully agree with Mr:  Duncan Robertson