How is the Interface Segregation Principle different from the Single Responsibility Principle?

SRP is about a class having exactly one reason to change — it's a rule about how a class's own responsibilities should be scoped. ISP is about an interface not forcing the classes that implement it to depend on methods they don't actually use — it's a rule about how a contract's shape affects every implementer of that contract. A class can perfectly satisfy SRP while still being harmed by an ISP violation: a SimplePrinter class with the single, focused job of printing can still be forced to implement scan() and copy() methods it has no use for, if the Machine interface it implements bundles unrelated capabilities together. In short, SRP is scoped to a class's own job, while ISP is scoped to how well an interface's shape matches what each of its implementers can genuinely support.