I attempt to show that the 'Large' argument of Parmenides 132 must be understood as part of the attempt to clarify Socrates' response to Zeno. The threat to that response is to the requirement that each form be one and not many. But it is also a threat to the very idea of having a share of a form. In context, the argument is underbrush clearing, getting an unworkable idea out of the way.
Turnbull, Robert G., "The 'Third Man Argument' and the Text of the Parmenides" (1983). The Society for Ancient Greek Philosophy Newsletter. 122.