"compare with " --- when it refers to the act of examining two like things in order to discern their similarities or differences:
当涉及考察两个相象的事物以辨别他们的相似或差别时，它取with ：
The police compared the forged signature with the original.
警察将伪造的签名与原来的作比较。
"compare to" -- when it refers to the activity of describing the resemblances between unlike things:
当它涉及描述不同事物相似性的活动时，Compare 常用介词 to ：
He compared her to a summer day.
他将她比为夏天。 | 
