Tumblr does not support a native comment function for blogs. If you want to comment on Tumblr, use the third-party program by Disqus, which Tumblr recommends and is enabled on many available templates. If you want to leave a message about an individual post, you can leave a reply on a Tumblr post.
Commenting on Tumblr
Tumblr comments are very similar to blog comments because they're messages that you can leave attached to the blog itself instead of to the individual posts. Comments don't move from blog to blog in the same way that replies to posts do. Tumblr recommends adding Disqus to your blog if you want a comment feature, which is one way to get feedback on your individual Tumblr account.
Replying on Tumblr
Unlike comments, replies are built into Tumblr and don't need to be added to the template. They aren't enabled by default, so click the gear icon on your dashboard, click your blog name and then click the two check boxes to enable post replies from those you follow and followers. To leave a comment on a Tumblr post from your dashboard, click the speech bubble icon, type your reply and then post it. If you're reblogging it from its own page, click the reblog icon and leave a comment on it before reblogging. If a user doesn't have replies enabled, you can't leave a reply on his posts.
Both comments and replies can be viewed by anyone on Tumblr as long as your posts and blog are public. Only secondary blogs can be password-protected, so if you want hidden comments, add the Disqus comment feature to a secondary blog instead of your primary Tumblr. If you want an individual to not see replies you leave on a Tumblr account, block him. That won't prevent him from seeing comments, however, since commenting is managed by Disqus and not Tumblr.
To add the Disqus comment functionality to Tumblr, open your Tumblr dashboard and click the gear icon to access Settings. Click on the name of the blog that you want to enable comments on and then click "Customize." Type your Disqus shortname into the Disqus field and click "Save" to finish. If you use a template that doesn't offer Disqus support, you can still install Disqus by adding some code to the HTML of your template.
Another way to solicit comments on Tumblr is with an ask post. Anyone with a Tumblr account can answer the post once you've created it. To make an ask post, click "Text" and type a title that ends in a question mark. Click the box next to "Let people answer this" to enable answers. If you want to leave a comment on an ask post, sign in to your Tumblr account and visit the blog where the ask is posted and then click "Answer."
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