By  reflecting  on  how  each  of these  purposes  can  play  a  role  in  the classroom,  which  kinds  of  sources  are appropriate  for  each,  and  where  they  fit into  an  overall  sequence  of  instruction, teachers  can  ensure  that  their  use  of sources  deepens  and  extends  students' historical understanding. These purposes are 1) illustration and motivation; 2) evidence for historical inquiry; 3) visual or  textual  interpretation;  4)  source analysis.