External is similar to Outside. Outside is related to Edge. Edge is related to Shape. 
Will is similar to Shall. Could is etymologically related to Shall. Could is related to Able. Able is related to Willing. 
External <--SimilarTo--> Outside <--RelatedTo--> Edge <--RelatedTo--> Shape 
Will <--SimilarTo--> Shall <--EtymologicallyRelatedTo-- Could <--RelatedTo--> Able <--RelatedTo--> Willing 