We’ve already discussed the importance of a canonical tag in prioritising duplicate pages. However, it is important to understand the reason for this tag. When you have more than one page with the same content, a search engine crawler does not know how to prioritise. It will often choose the wrong page as most important or split query results between the two. Both of these can be disastrous. The canonical URL tag should be used whenever there is more than one of the same page. In addition, you should avoid giving contradictory canonical tags–that is, marking two of the same page with the tag–because this negates the benefit of the tag.