Both of them are religiously different from each other. So, let’s see the major difference between a forum and a blog on a side by side comparison.
Forum:
Forum is User Generated Content.
Members participate in the discussion to share views and ideas.
Can take the form of question and answers.
One can’t trust the worthiness of the forum replies.
Forums are much easier to generate content.
You always need to monitor the forum for moderation.
Blog:
Blog is an Author Generated Content.
Author share views and ideas on the blog topic.
For questions, one has to ask the blogger, and he may answer readers’ questions.
Bloggers tend to build the trust of the readers and share views and ideas that are trustworthy.
Blogs need a lot of time on research before an author can write about the topic.
You don’t always need to be blogging.
Blogs heavily depend on the expertise of the author. On the other hand, forums can have millions of authors, but it relies heavily on member’s interactions.