 As Williamson (2000) notes, the idea that we can extend our knowledge by applying deduction to what we know supports a closure principle that is stronger than K. It is a principle that says we know things we believe on the grounds that they are jointly implied by several separate known items. Suppose I know Mary is tall and I know Mary is left handed. K does not authorize my putting these two pieces of knowledge together so as to know that Mary is tall and left handed. But the following generalized closure principle covers deductions involving separate known items: