When only 1 attribute value, is not shown.

Dear all,

I have variable products and I have some attributes for each product. Assume that I have an attribute size S, M, L. In the case where the attributes values are more than one that are available, then is correctly shown.
however in the case where I have a t-shirt for example where only the M size is available then it doesnt show it at all. In that case the customer does not know what size is the product he is looking. I want to show the attribute values even when there is only 1 value available.