WordPress is_blog()

is_blog.php

function is_blog () {
	global  $post;
	$posttype = get_post_type($post );
	return ( ((is_archive()) || (is_author()) || (is_category()) || (is_home()) || (is_single()) || (is_tag())) && ( $posttype == 'post')  ) ? true : false ;
}


Usage: 

 <?php if (is_blog()) { echo 'You are on a blog page'; } ?>

How about this?
in fact, is_singular() is the same as if ( is_single() || is_page() || is_attachment() )

if ( is_singular( 'post' ) ) {
	echo 'You are on a blog page'; 
}

Taking @grantnorwood's code from 2012:

• The ternary return is unnecessary so let's just return the comparisons.
• Also, $post_type == 'post' is the cheaper operation so let's put it first.
• Finally using triple equals as there should be no type conversion.

/**
 * WordPress' missing is_blog_page() function.  Determines if the currently viewed page is
 * one of the blog pages, including the blog home page, archive, category/tag, author, or single
 * post pages.
 *
 * @return bool
 */
function is_blog_page()
{
    global $post;

    // Post type must be 'post'.
    $post_type = get_post_type($post);

    // Check all blog-related conditional tags, as well as the current post type, 
    // to determine if we're viewing a blog page.
    return ( $post_type === 'post' ) && ( is_home() || is_archive() || is_single() );
}

Has anyone noticed that this fails when there are no posts assigned to a tag or category? $post is NULL when you visit a category/tag archive that has no posts to display. I've been using this for years and seen it on and off - i mostly use this just for page titles, which weren't showing in this case. I never looked into it because usually the categories/tags fill up with posts and it's not an issue! But clients sometimes...