The simplest and most illuminating example of eigenspinors is for a single spin 1/2 particle. A particle's spin has three components, corresponding to the three spatial dimensions: S x , S y , and S z . For a spin 1/2 particle, there are only two possible eigenstates of spin: spin up, and spin down. Spin up is denoted as the column matrix: χ χ + = [ 1 0 ] and spin down is χ χ − − = [ 0 1 ] .