Adverbs are concepts of the characteristics of motion (or action); they are
formed by specifying a characteristic and omitting the measurements of the
motion and of the entities involved—e.g., “rapidly,” which may be applied to
“walking” or “swimming” or “speaking,” etc., with the measurement of what is
“rapid” left open and depending, in any given case, on the type of motion
involved.
Prepositions are concepts of relationships, predominantly of spatial or
temporal relationships, among existents; they are formed by specifying the
relationship and omitting the measurements of the existents and of the space or
time involved—e.g., “on,” “in,” “above,” “after,” etc.
Adjectives are concepts of attributes or of characteristics. Pronouns
belong to the category of concepts of entities. Conjunctions are concepts of
relationships among thoughts, and belong to the category of concepts of
consciousness.