if you change one of the selectors to have a different than the others, this will break down and you may get unexpected results.
a:link { color: blue; text-decoration: none; }
a:visited { color: purple; }
/* if user hovers over visited link, hover styles take precedence */
a:hover { text-decoration: underline; }
/* if user clicks link, active styles take precedence */
a:active { color: red; }