“I want to focus on the comparison between {{w|spinor}}s and the {{w|complex number}}s. Complex numbers... took mathematicians several hundred years to really feel they understood what i was. i is the {{w|square root}} of {{w|-1}}, what is called an {{w|imaginary number}}. It did not exist, but they found it very useful. They used it in formulas, and gradually, step by step, it became accepted... [F]inally the formal definitions were given so i... became and accepted part of mathematics, but it took a long, long time.”