Justin: As usual, an excellent explanation for a seemingly complex subject. Count me as a subscriber!

Great summary of an oft-confused topic Justin.

Why not just set Categories and Archives to not be indexed? See any drawback to that?

Thanks that helped a lot and as I said in Robert’s post, my client from Google had told me this summer when we closed on his house that Google would not penalize for duplicate content on blogs that you personally own and he said up to 3-4.

He said the real thing Google hates is web sites that are all template with no variety in content.

I did a post yesterday on my blog, and it covered 3 categories, Ann Arbor, Events and Saline. All were valid in the post. So today, I have had 4 different Google Alerts is the category thing why?

@Missy - You’re probably getting google alerts because you mentioned all three of those keywords in the post itself.

@Jay - Yes, I suppose you could use robots=noindex on your category pages, but I find that categories are often great landing pages for search engines. But you could use it on archive pages since they are mostly useless in ranking anyway.

Finally an explanation that makes sense! I’ve been wondering about this since last April. Thank you for the clarification.

Thank you for clarification Justin. I’ve heard this discussed, and even talked with you about it, but I’ve never seen a good explanation published. Thanks for bringing up the issue. I used to think it was better to put a post in more categories. I feel better being sure of what I am doing.

Great explanation. I read Roberta’s post and then went immediately to my blog and edited some of the categories! How to keep up with it all?

I know loads of people that post duplicate content all over the web. Most say that it doesn’t affect their pages…but what will happen the day that alorithm changes? I think Google will hand out Gimp Slaps to these people.

This topic is always confusing and most of the time misunderstood. You have presented in a clear, understandable fashion. Thanks. I think some people try to talk when they don’t exactly know what they are talking about.

The Google duplicate content thing is mostly a myth, but I agree with a potential change in algorithm. You never know when those smart guys at Google will figure a way to potentially penalize sites if it looks like duplicate content is originating from a single source. Keeping your nose as clean as possible is the most prudent course of action.

I think Google penalizing duplicate content is a great idea. Otherwise people would just copy and paste content all over creating even more spammy sites.

Even if you don’t get penalized by having the content duped on your own site, it seems to me that your PR will become a bit diluted if you have all of that link-rich content appearing in multiple places. I prefer to keeps the robots away from category pages so that I can save that PR for something better.

Very interesting, I never even thought about having my content in more than one category being a big deal at all. Thanks for the info!

Great post, I never thought about duplicate content in that manner. Time to add nofollows

Justin very concise in your explanation. I read the post you are refering to and noticed people were confused based on the comments as well. In the case of AR what would be considered the blog home page?

On AR, a blog home page would be something like this: http://activerain.com/blogs/hismove

And on AR, your tags act similar to the way categories do on a normal blog.

At PubCon this was talked about by some bloggers that make serious money doing so. They made it pretty clear that in the long run you need to figure out how to keep it so there is only one version of the post that Google is seeing. Great post.

This explanation on onsite duplicate content has helped much and I look forward to a post on offsite duplicate content if you are doing one.

I have my blog posts and web pages copied verbatim and the copy cats rank their copied pages higher than me. Makes me sick.

Thanks for the thorough explanation about duplicate contents on the blog. If duplicate content is not penalized, I think people will just copy and paste articles and publish as their own.

there are a few plugins that you can install in wordpress to stop google indexing catergory and archive pages. this will mean that duplicate content on your blog would be minimised.

i think the best plugin for this is all-in-one-seo-pack

Thanks for the clarification. I would place posts into different relevant categories with the idea that I wanted to make sure people could find. Now I understand that I could actually be doing myself a disservice.

Thank you for explaining this to me. To me this was a very confusing subject. I corrected my blog this morning.

Thanks for clearing that one up,
It has baffled me for a long time.
I went stupid on some of my posts when I first started, putting them in 6-7 categories. How much damage does it do if I remove categories after time?

Great Post by the way.

Hey Justin,
Nice post, I’ve been considering this for some time now. I’m thinking that using subcategories will help me keep things organized but I worry I may run into the same problem as using multiple categories for a single post. That is, wouldn’t a post that’s assigned to a subcategory also appear in the main category archives too? Thus we’re right back where we started. Any thoughts on how to do use subcategories while avoiding the duplicate content issue?

PS. If you could add the option to subscribe (via a plugin) to comments on posts that would be great!

Noindexed categories and archives via Robots Meta plugin by Joost de Valk. Thanks for the advice Justin!