The Soul Urge, sometimes called the Heart's Desire, is taken from the vowels of the birth name and read as what a person wants when nothing is watching. The Minor Soul Urge runs the same calculation over the name the person actually uses. The vowels of the working name are summed, the consonants ignored, and the total reduced to one figure, with the master numbers eleven, twenty-two and thirty-three left standing.
Of the three minor positions this is the one practitioners treat most carefully, because the claim behind it is the strongest. The Soul Urge is supposed to describe something interior and given, and it is not obvious why adopting a shorter form of your own name should alter it. The usual answer in the literature is that the minor figure describes not a change in what a person wants but a change in what they are currently able to want: the desire as it is available to them in the life the working name belongs to.
Whether that distinction survives examination is a fair question, and it is the sort of question the tradition does not settle by argument. What the position gives practically is a reading in which the birth name and the working name are held together, with the gap between them treated as the finding. A person whose two Soul Urge figures diverge sharply is described as living at some distance from what they most want, and the reading is built on that gap rather than on either number alone.