Socrates continually insists that Euthyphro provide that one feature which all holy deeds have in common—by which they can all be defined. This insistence is similar to that which underlies the Theory of Forms, and Plato even employs much of the vocabulary that he would later use in discussing his famous theory in later works, such as Phaedo.
However, everything about the structure of Euthyphro suggests that it is an early dialogue, which would make the inclusion of the Theory of Forms an impossibility. The ideas expressed in Euthyphro can make perfect sense without being framed in terms of the more complex, later theory. If we were to read the Theory of Forms into Euthyphro, however, we could identify Euthyphro's ultimate failure in defining holiness as being a failure to recognize the Theory of Forms. The feature that all holy deeds have in common is the Form of Holiness, according to the theory, and any other definition of holiness will be unsatisfactory.