The potential values for a conditionally defined variable must all share a data type. If you have 2 richtext variable and 1 shorttext variable, you won't be able to use all 3 in a conditional. Unless you recast the shortext variable into a richtext type. This FAQ will show you how.
Text Blocks are a type of logic block that define a richtype variable.
Now you have 3 richtext variables which you can use in your conditional.