Whenever possible, in writing an outline, coordinate heads should be expressed in parallel form. That is, nouns should be made parallel with nouns, verb forms with verb forms, adjectives with adjectives, and so on. Although parallel structure is desired, logical and clear writing should not be sacrificed simply to maintain parallelism (For example, there are times when nouns and gerunds used at the same level of an outline are acceptable.) Reasonableness and flexibility of form is preferred to rigidity.
The 'underground railroad' was known as such due to the slaves using it to escape and the people helping them to escape using secret codes that were commonly associated with railroads.
(Ex: 'station masters' = people who would hide slaves)
