Multiplicity in Unity

Leibniz's concept in this passage from the "Monadology" delves into the complex idea of monads and how change occurs within these indivisible, simple substances. Monads, according to Leibniz, are the fundamental units of reality—simple, indivisible, and imperceptible. They do not have physical parts but are the basic elements of all matter.

The key points to understand from this passage are:

1. **Multiplicity in Unity**: Even though a monad is a 'simple substance'—meaning it has no parts—it can embody a multiplicity of qualities or properties. This reflects Leibniz's principle of "the identity of indiscernibles," which states that no two distinct things exactly resemble each other. Each monad is unique and contains within it a reflection of the entire universe, but in a unique way.

2. **Gradual Change**: Change within a monad does not occur all at once but gradually. This is crucial because it implies that there is a form of continuation and transformation within each monad that does not disrupt its fundamental unity.

3. **Persistence Amidst Change**: Despite these changes, the core or the essence of the monad remains unchanged. This aspect touches on Leibniz's argument against the concept of void or vacuum and absolute motion, suggesting instead that change in substance always involves both a degree of alteration and persistence.

4. **Relational Affectation**: Although monads have no physical interaction with each other—since Leibniz posits that the monads do not physically affect each other—they are still interrelated in such a way that the changes in one reflect changes in the experience or state of others. This is due to the pre-established harmony set by God, ensuring that every monad mirrors the universe in a synchronized fashion.

Leibniz's Monadology offers a complex metaphysical view where even the simplest substance is teeming with internal activities and relations. Understanding these dynamics sheds light on his broader philosophical endeavors to explain the order, harmony, and connectivity of the universe without recourse to physical interaction among its fundamental components.