Numerology tends to split a full birth name into two useful halves. The vowels feed the soul urge number, traditionally read as inner motivation. The consonants feed the personality number, traditionally read as outward presentation — the surface a name shows the world.
Both use the same Pythagorean letter-to-number chart, and both reduce the same way: sum the relevant letters' values, then collapse the total to a single digit, unless it's a preserved master number.
The logic behind the split is more symbolic than technical. Consonants are treated as a name's structure — the hard consonant sounds that shape how a word is heard — while vowels carry something closer to feeling. It's a tidy metaphor more than a proven mechanism.