Salazar Slytherin's books were among the few that treated both halves of the mind arts as a single discipline, which meant they could be used for healing just as easily as they could be used for intrusion, assuming the reader knew what they were doing. Julian opened one of those volumes and was almost immediately pulled into how carefully the information was recorded. The writing was precise, orderly, and far more thorough than he expected.
He learned early on that Occlumency and Legilimency had once been taught as one subject. Only later had they been separated into two fields based on their practical outcomes.
Legilimency was described as the art of reading and influencing the minds of others with care. It demanded refinement and restraint, a delicate touch and absolute control. Slytherin made it very clear that forcing one's way into another person's mind was the mark of an amateur, or worse, someone who simply did not care what damage they caused. His disdain for that kind of practitioner was obvious on the page.
Occlumency, by contrast, was the art of mastering and protecting one's own mind. Because it focused inward, it was more tolerant of mistakes. Failures were still failures, but the cost of them was less catastrophic than fumbling around inside someone else's head. Slytherin also made it plain that he believed every wizard should possess at least a basic foundation in both aspects of the mind arts.
...
The book covered the same starting principles for Occlumency that Julian had seen in the earlier text, but with far clearer detail, the sort that actually told him what to do instead of vaguely gesturing at enlightenment. It also recommended learning Legilimency first, before trying to build serious shields. The reasoning was simple. It was easier to defend yourself once you personally understood how an attack felt and how it moved.
To begin training in Legilimency, a student first had to decide which form they intended to pursue, because Slytherin insisted there were two distinct variations, each with its own strengths and weaknesses.
The first was silent Legilimency, the kind that relied on eye contact without any spoken incantation.
This form required the caster to learn wandless casting and to project mental tendrils through the eyes. That was why it was often assumed to be something only masters could achieve, when in truth it could be learned independently without ever mastering the other form. Its advantages were obvious. It was quiet, it could be started quickly, and if the target did not realize they were being probed, it could be difficult to detect.
Its drawbacks were just as clear. It was weaker than the second form, easier to block once noticed, and the concentration it demanded left the caster exposed to retaliation.
...
The second form was the one the discipline was named for, the wand based spell spoken aloud, "Legilimens," using the wand as a conduit into the target's mind.
Its advantages were stability, power, and precision. The wand gave structure to the magic, making it stronger and easier to shape.
The disadvantages were equally important. Anyone nearby would know what you were doing the moment they heard the incantation. Using it on someone without permission was illegal. It also placed greater strain on the caster's mind because the working was forced through a focused channel rather than spread naturally.
...
Slytherin went out of his way to emphasize how much good the art could accomplish when used properly, from easing mental illness to making Muggles overlook something they were never meant to witness. According to the book, the Obliviate charm had been developed based on Legilimency's capacity to alter memory, intended for witches and wizards who were unskilled in the deeper mind arts, or simply in too much of a hurry.
Obliviate worked by removing the memory directly from the part of the mind that stored it, erasing it outright. In the hands of a skilled caster, it could be done so smoothly that the victim did not even realize something was missing.
The Confundus charm, on the other hand, prevented the mind from forming new memories altogether, which made it ideal for situations like slipping into restricted areas past guards. The person would remain unaware, but the mind would fail to record what was happening.
...
Slytherin then laid out novice training in both forms, step by step, with the kind of practical structure Julian had been looking for. First, the student needed to become accustomed to controlling mental energy. The best practice target, according to Slytherin, was a simple insect, something like a fly or an ordinary beetle. Once that control was stable, the student was meant to move on to larger and more complex creatures, rats first, then cats, then dogs.
Slytherin strongly warned against the trap of experimenting on humans as a beginner. Not only because of the danger to the victim, but because the rapid progress it offered came with a hidden cost. That shortcut traded away the deepest potential of the art.
If a practitioner refused to use Legilimency on people and instead advanced through increasingly powerful magical creatures, the final ceiling was higher. In the end, such a legilimens could potentially use the art even on something as mighty as a dragon.