According to Webster’s, a “science” is "a body of knowledge covering general truths or the operation of general laws especially as obtained and tested through the scientific method.” 

Also according to Webster’s, the scientific method involves “principles and procedures for the systematic pursuit of knowledge involving the recognition and formulation of a problem, the collection of data through observation and experiment, and the formulation and testing of hypotheses.” 

Therefore, to pass muster and qualify as a science, a discipline must embody (1) principles that apply universally, (2) testing procedures that produce identical results in any language, under all different forms of government, during feast or famine, at any latitude or longitude, and so on, and (3) practitioners who can make predictions in their field with 100% accuracy or close to it. 

So chemistry, physics, metallurgy, biology, and so on all fit that bill. Psychology and psychiatry don’t. And by the way, while I’m at it, neither do economics, political science, sociology, and a host of others. 

You know, I really don’t want to belabor the point. So here's the clincher. 

It’s not uncommon in a legal proceeding for three psychiatrists to examine a defendant and find him sane while another three examine him and find him insane. 

Now can you imagine three physicians examining a defendant and finding him alive while another three examine him and find him dead? 

I rest my case. 

Think about it.