What happens if two authors have the same last names? In that case, you use the initials of their first names, or their full names if they have the same first names, so that it is clear in your text which author you mean. So, if you cite both Karl Marx and Groucho Marx, you would use the initials of the first names in the citations, even though the years of publication are different.
(K. Marx 1853:334)
(G. Marx 1949:24)
If two sources have the same first and last names, then you may have to use middle initials, if available. The general rule is always to try to give enough information so that the reader will know exactly what individual or publication in the reference list you are referring to.
