Complex sentence: Thus perceptions must already come parcelled into distinct "bundles" before they can be associated according to the relations of similarity and causality: in other words, the mind must already possess a unity that cannot be generated, or constituted, by these relations alone.
Split into simpler sentences: Thus perceptions must already come parcelled into distinct "bundles" before they can be associated according to the relations of similarity and causality. In other words, the mind must already possess a unity that cannot be generated, or constituted, by these relations alone.