(Disclaimer: This line of thought is very much a very a work -in-progress, incomplete and certainly not conclusive in my understanding. I'm trying to describe here what prototyping implies as a process in the context of design thinking, so bear with my going "meta" here, as Bill Buxton put it.)
I'm more interested in distinguishing between Hacking Vs Prototyping, as I increasingly see the two confused by younger professionals, especially with the global startup frenzy now on. I'm responding here to the widespread and rather loose use of the word Hack. Btw, for the culturally curious, there's a specific Hindi word for Hack: Jugaad.)
A hack is something quickly put together by combining pieces from other things. You usually know what you are going after. You have an outcome in mind.
So if you tie a belt to a backpack to help you carry it better, its a hack. You kind of knew the outcome you were going after when you picked up that belt.
A prototype, by contrast, is something subtly different. To summarise what I consider prototyping, I'll lean in on the immortal words of Lao Tzu: "If we don't change direction, we'll end up where we are going."
Prototyping is a process of understanding by making. It chases the question: what's possible here? It's a childlike, open-ended exploration of possibilities, fuelled by a open imagination, and guided by the uncanny intuition of a craftsperson. Such intuition gets better with experience, and with failure.
At the risk of sounding convoluted, I claim that a prototype is the solution you already hold in your hands seeking a problem.
A prototype is potential seeking purpose.
Prototyping is the process of using existing materials to seek disruptions in the environment and discontinuities in experience .
No wonder some of us see prototyping as an art rather than a science. The key is to be in a position where you are not constrained by an overbearing problem that you need to solve. So with a backpack and belt, you'd ask: what can I make with this? Imagine the possibilities. Your first impulse would be take it all apart and find its component pieces. It would be destructive creation. Thats the reason prototyping and synthesis go together in the design process. Now imagine the possibilities if your materials were digital technologies, data, and human behaviour.
Clearly, real prototyping needs time, resources, skills and experience. True prototypes are usually funded by R&D, not Product or Marketing.
Prototyping is commonly seen as the process of realising a product in small increments. And that's fine. But knowing when you are really prototyping, compared to when you are actually hacking, is a very valuable distinction to have in the design innovator's toolkit.
This is especially valuable when trying to find ways to commercialise a new technology. In tech commercialisation, you'd have to know when to stop prototyping and start hacking. You'd change direction from what's technically possible to what's behaviourally desirable. This is where you'd need behavioural insight and input.
An interesting thing: it is hard to tell from looking at a product if it is an outcome of a prototype or a hack. That's the reason a lot of designs are presented as prototypes, when they are actually hacks. The best way to be sure which is which is to be involved in the making.
A guideline: prototype to open up possibilities, and hacks narrow them.
P.S. I think that the latest Apple product, the Watch, is essentially a prototype. In looking through the narrow lens of existing 'use cases', we tend to scrutinise it and conveniently label it a 'solution'. We should rather see it as a probe - designed to learn as much as it can about its wearer and the environment she resides in. Part of the design genius of Apple is in getting people to pay an insane amount of money to own a prototype, and simultaneously pat themselves for being continuously innovative as a company.