One of the primary lessons I learned from your book, Emotional Design, is that designing products to induce certain emotions can make them more usable, can increase their functionality if you like. In many ways I could see how this would indeed aid Inclusive Design, as the idea is to make products more usable for a wider range of people: e.g., one could emotionally design a product to make it easier for elderly people to use.
On the other hand, in Chapter 2, you also talk about the need for 'market segmentation', which is something contrary to the who idea of 'design for all'. I don't personally believe one can design a single product that will please everyone, but I know that 'inclusive design' is about maximising the potential market by designing products that are more appropriate for those who were previously excluded by inappropriate design (e.g. elderly or disable people)
I just wondered what your thoughts might be on the relationship between these two design fields, if there is one at all?
An excellent question. Design for All is a laudable goal (also known as Universal Design). In general, Universal Design focuses upon physical requirements: visibility and legibility, physical dimensions, gripping, and so on, factors that are required to overcome limitations in size, mobility, strength, or the lack of limbs, or difficulties with vision, hearing, or speech. These all fall into the "Behavioral Design" level of Emotional Design. I strongly support these goals.
As you properly point out, although no single product will please everyone, at the behavioral level, Universal Design can maximize the market by including those who would otherwise not be able to use the product. Also note that invariably when we design something that can be used by those with disabilities, we often make it better for everyone.
But when it comes to the emotional side of design, most especially, Reflective Design, then I believe that we must design separately for different target populations. Mind you, these distinctions are more apt to be cultural than physical. Thus, Chinese teenagers might prefer a very different mobile phone than European business people, and these distinction might very well apply even if some of the people have disabilities.
Consider how the three three levels of design apply to people. We must ensure that products are Viscerally attractive, Behaviorally functional, and Reflectively desirable to all populations, even if this means different products for different groups. But even as we do different products for different market segments, each should follow the principles of good behavioral design, which means following the principles of Universal Design, among other things.
In my opinion, no single design is apt to be optimal for everyone. This is true whether we are talking of behavior issues, visceral ones, or reflective ones. Market segmentation s a natural result of the vast differences among people.
I see no contradiction in the philosophy of Design for All" and the market segmentation that might be required for Reflective Design. Put it this way: just because two people might have the same disability in no way implies they have the same likes and dislikes. They are much more apt to like the same items that other people of their same age, cultural background, and interests like, even if the others do not share the disability. Good design requires consideration of all aspects of human beings: the behavioral (hence Universal Design), the Visceral (hence, attractive style), and the Reflective (hence, cultural differentiation).