Difference between written description and enablement

In a lot of file histories that I read, both practitioners and Examiners seem to confuse the written description and enablement requirement, conflating the two into a single requirement that "claim terms must have support in the spec."

Maybe there's good reason to be confused. The recent en banc decision by the Federal Circuit in Ariad v. Lilly affirmed that these two requirements are separate, but also suggested that the two requirements can be confusing. The majority recognized that in some fields "there is little difference between describing an invention and enabling one to make and use it" and that "written description and enablement often rise and fall together."

I read a recent blog post at Intellectual Property Directions which included this concise summary of the difference between written description and enablement, put in terms that anyone can understand:

In effect the [Ariad v. Lilly] court said that a pure enabling description was like a bare bones cookbook recipe in which the how to make is included but you are never told what you are making! Take flour, sugar, shortening, leavening, and water, mix them until smooth, and bake for 1 hour at 325 degrees in a greased cake pan. You can follow the steps but it’s up to you to guess what it is you are serving. Without a written description you almost have to try it to find out if it’s a cake or a giant cookie.
(from If it walks like a duck… you need a written description)

Thanks to blogger Bruce Horwitz for coming up with this explanation.