Tumblr has its own specific features and functions that aren’t necessarily comparable to other social networks and blogging platforms. For example, Tumblr blogs use “replies” in lieu of a traditional comment system. To reply to a post on Tumblr, the blog owner must enable replies from people following the blog for at least 10 days or people the blog owner follows. It is also possible to enable both. A “Reply” link is visible on posts on your Dashboard to which you can reply.
Not So Fast
Replies are intended to leave a quick comment or thought on a post, as Tumblr has its “Ask” feature for questions and answers. First, you can only reply through the Dashboard and not through a post’s permalink page. Second, neither followers nor the blog owner can answer replies on a post. Tumblr does support Disqus, a universal comment system. If a Tumblr blog has Disqus enabled, you can create a free account and reply through that.