Ideal System

Given our definition of ideality as the ratio between a system's useful functions and its harmful functions, we can imagine an ideal system as a system that has no harmful functions at all -- in other words, it costs nothing to design or maintain, uses no energy, takes up no space, has no harmful emissions or byproducts, and so on. Or, stated another way: An ideal system is one whose functions are performed without the system existing.

Actually, we don't need the system at all -- what we need is its function. (For example, it's not the steering wheel we need, but some means of controlling the car.) What's more, all harmful effects are associated with the system rather than the function.

Of course, this is an ideal image. In reality we can only aspire to it. Often, however, we can come fairly close to the ideal.