#15: the_content

the_content.php

<?php
/**
 * Convert double-spaced sentence endings to singles
 * 
 * @param string $content The post content.
 *
 * @return string The filtered post content.
 */
function wpdocs_double_spaces_to_singles( $content ) {
	// Replaces '.  ' with '. '
	$content = str_replace( '.  ', '. ', $content );
	return $content;
}
add_filter( 'the_content', 'wpdocs_double_spaces_to_singles' );

http://fotd.werdswords.com/the_content/