[Tex/LaTex] getting an option clash with Babel, [english,greek]

Question

I am getting an option clash for babel using: \usepackage[greek,english]{babel}. Here is the output:

! LaTeX Error: Option clash for package babel.

Does anyone know what might be causing this? I've tried Googling and have seen many others use these options together, but I cannot get it to work. Here is my full latex heading:

\documentclass[article,11pt]{Latex/Classes/PhDthesisPSnPDF}
\raggedbottom
\setcitestyle{square}
\usepackage[normalem]{ulem}
\usepackage[greek,english]{babel}
\usepackage{amsmath}
\usepackage{amstext}
\usepackage{wrapfig}
\usepackage{graphicx}
\usepackage{algorithm}
\usepackage{algorithmic}
\makeatletter
\def\NAT@def@citea{\def\@citea{\NAT@separator}}
\makeatother

Answer 1

It's because the class you're using (available here) already calls babel with the english option. The solution is to pass the greek option when loading the class file with

\documentclass[greek,<...>]{<class>}

You could also call it with a \PassOptionsToPackage{greek,english}{babel} before loading the package, therefore before \documentclass, since the class is loading it.

See:

• Conflict between Options of Packages;
• Heiko Oberdiek's answer to Passing options to loaded package not working with Beamer class;
• "Option Clash for Package" at the TeX UK FAQ