There’s an email that floats around, especially among those of us who have children or siblings or other loved ones with mental disabilities. It is sweet and endearing and describes an adult woman’s love for her brother. Early on, she says his mental age is 8.

She goes on to explain what he does every day–gets up and gets dressed, eats breakfast, gets on the bus and goes to work. Does his job. Comes home in the evening.

The point of the email is to attest to the value of her brother’s life no matter his mental capacity, and I agree with the author’s point. And yet I take issue with the idea of “mental age.” What 8-year old goes to work every day? This woman describes a mature adult as much as she describes an elementary school student, and yet as soon as she uses the words “mental age of 8,” readers are inclined to equate him with a boy in the third grade.

I used to be afraid, when I read emails or articles or books that mentioned the “mental capacity” of people with Down syndrome. I used to be afraid that my daughter would never grow up. But I’ve realized with time that Penny, and her peers with disabilities, will indeed grow up. They will become adults, with areas of weakness, and with areas of maturity too.

I’m sure the woman who wrote that email loves her brother very much. And I’m sure she knows him as an adult, not as an 8-year old.

It is so easy to reduce ourselves, and each other, to something measurable, quantifiable. And it is so dangerous when we do.