Crawl Issue Found: No rel="canonical" Tags

[fdmgroup]

Given that google have stated that duplicate content is not penalised is this really something that will give sufficient benefits for the time involved?Also, reading some of the articles  on moz.com they seem very ambivalent about its use – for example http://moz.com/blog/rel-confused-answers-to-your-rel-canonical-questionsWill any page with a canonical link normally NOT be indexed by google?Thanks.

[David-Kley]

Google has stated that duplicate content will be penalized, if it is deemed that the content is meant to manipulate search results. https://support.google.com/webmasters/answer/66359

"In the rare cases in which Google perceives that duplicate content may be shown with intent to manipulate our rankings and deceive our users, we'll also make appropriate adjustments in the indexing and ranking of the sites involved. As a result, the ranking of the site may suffer, or the site might be removed entirely from the Google index, in which case it will no longer appear in search results."

If two pages both have the same content, even with a canoical url Google will choose which one to index most likely the newer version of that page.
"Google tries hard to index and show pages with distinct information. This filtering means, for instance, that if your site has a "regular" and "printer" version of each article, and neither of these is blocked with a noindex meta tag, we'll choose one of them to list."

I would not recommend having duplicate content on your site if it can be avoided. If it can't, set one of the pages you dont want indexed to "no-index".

[fdmgroup]

Thanks. Should I add the canonical tag to all pages on the website? And how do I do this in WordPress SEO?

[KarlBantleman]

A canonical tag tells Google that you are aware of the duplicate content that exists on your website and you are telling Google which page to count as the authority. Pages with a canonical tag WILL be indexed.

Websites with duplicate content can, have and will be penalised by Google, that is what Panda is all about. The canonical tag does fix this in the majority of times but if there is a way of removing any duplicate content then this is advisable.