Original sentence: The division of related languages into sub-groups by the comparative method is accomplished by finding languages with large numbers of shared linguistic innovations from the parent language; two languages having many shared retentions from the parent language is not sufficient evidence of a sub-group
Edited sentence: The division of related languages into sub-groups by the comparative method is accomplished by finding languages with large numbers of shared linguistic innovations from the parent language; two languages having many shared retentions from the parent language is not sufficient evidence of a sub-group (analogous to synapomorphy and symplesiomorphy in biological phylogenetics)