"Every idea originates through equating the unequal" (pg. 91). This is stated by Friedrich Nietzsche in "Philosophical Writings". But what does he mean by it? Perhaps an example will shed some light. No two leaves are alike, yet when one person says 'a leaf', another person will understand, but in their own idea of what a leaf is. So the idea of what a leaf is formed. This implies that there should be a universal leaf: one that with all its properties all other leaves originated from. Therefore the leaf is the cause of leaves. If this sounds familiar, then you are correct: a primal universal is a recurring idea in philosophy.
If that sounds too far fetched or ancient, take a look at it with the universal language: mathematics (which doesn't lie). If Jack and Jill were to draw a triangle, both of their drawing could be different. Jack may draw a small isosceles triangle and Jill may draw a large right triangle. If you break down what a triangle is, you'll see that they are both the same. They have three angles which add up to 180 degrees, and that is the definition of the universal geometric figure known as a triangle. One could not argue that their idea of a triangle is incorrect, should you ask Jack and Jill to go out and return with a leaf, they will return with different leaves but a leaf none-the-less. Did either of them fail their mission? No.
"As no one leaf is exactly similar to any other, ...the idea 'leaf' has been formed through an arbitrary omission of these individual differences, through a forgetting of the differentiating qualities, and this idea now awakens the notion that in nature there is...a something called the leaf" (pg. 91). The leaf is the cause of leaves, just as the triangle is the cause of triangles. Everything is different, but by putting aside the minute differences you end up with an idea that is understood by everyone. Putting aside natural and geometric examples, you can find this theme of ideas in history. Look at a main driving notion for the Civil Rights movement: we may have different colored skin, but we all bleed red. We are all humans despite being slightly different.
So the concept of ideas forming from unequal ideas holds true. One may try to disprove the concept of a primal form, yet examples of it can be found in nature, history, mathematics, and in many other concepts. Perhaps this is the reason why this is a basis commonly seen in philosophy. It is false to say that your fingerprint is the same as my fingerprint, but when we both are at the police station and the officer says they'll be taking fingerprints, we both know exactly what he means by the conceptual idea of fingerprints.
