A curable composition includes a condensation product having a weight average molecular weight of 30,000 or less and a curing agent, the condensation product being obtained by hydrolysis and condensation of a first and secondsilane compound in the presence of a neutral salt catalyst. The condensation product also has a ratio Y/X of 0.2 or less, wherein X is the number of moles of an OR3 group directly bonded to silicon atoms of the first and second silane compounds, and Y is the number of moles of an OR3 group directly bonded to a silicon atom of the condensation product. The first silane compound is represented by R1—(SiR2a(OR3)3-a), and the second silane compound is represented by R4—(SiR2a(OR3)3-a).