In my rails website I want to make a form with nested resources.
More specificly, I want to add a comment section to my blogposts.

The solution I found on several places is creating a form with the rails helper form\_for and binding both the `@post` instance variable and the `@comment` instance variable to the form like this

```
<%= form_for[@post, @comment] do |f| %>

```

Now I was hoping that someone could explain me why it doesn't work to just bind it to `@comment`, even if you that comment has a foreign key to `@post`?
So in other words I still need to bind the form to both instance variables, even if I defined the following in my `show` action.

```
@post = Post.find(params[:id])
@comment = @post.comments.new

```

Rails is pretty smart, why isn't it able to figure out that `@comment` belongs to `@post`?