In text citations using "et al." when the first author is the same

The question:

"I'm using Harvard, and I have two sources with the same first author and the same year but different contributing authors.  In text, both would be (Cass, 2004).  Can I make one 2004a and the other 2004b? Or can I not do this because they have different contributing authors? If not, how do I differentiate between these two sources when in text referencing?"

The answer:

With in-text citations, you keep adding authors until the citations are clearly unique.  So, if you have the same first author, but different second authors, you would have (Cass, Cunningham et al., 2004) and (Cass, Devitt et al., 2004).

If the first two authors were the same, you’d add the third author to your in-text referencing – and so on.


The only time you use the 2004a/2004b option is if all of your authors are identical – the exact same authors in the exact same pattern.