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Writing Tips for Scientific Papers
by Susan Delap



Q. When should I use geologic vs. geological? Hydrologic vs. hydrological? ("-ic" and "-ical")
A. According to Suggestions to Authors of the Reports of the United States Geological Survey, Seventh Edition (1991), page 169:

The preference today is the shorter ending (hydrologic, hydrographic) but no strong justification supports such choice. Except for conventional expressions (Geologic Division, Geological Survey), consistency within a report should govern usage. "Historic," however, signifies momentous or ominous ("On this historic occasion"); "historical" means within the human cultural record and thus more accurately describes such natural events as earthquakes and volcanic eruptions, most of which were prehistoric. --Thanks to Jane Love, Managing Editor at the Bureau of Geology and Mineral Resources, for directing me to this reference. She says that the Bureau follows this preference in their publications.


Thanks to Lynda Walsh, Assistant Professor of English and Manager of the Writing Center at NMT, for providing some justification for the choices:

My understanding is if you're discussing data, you use geologic, as in "geologic time scale" or "geologic processes."  If you're discussing matters pertaining to the field--geology as a political community governed by shared conventions--you may use geological:  "geological methods," "geological ethics," "geological society."

Some other views:

  • Is it "-ic" or "-ical"?, by Marilyn A. Billone (USGS), in Blueline, Newsletter of the Association of Earth Science Editors, v. 33(1), Winter 2000, p. 3.
  • Random House: -ic, -ical in general


Links to Style Guides
American Geophysical Union (AGU) Style Guide
Chicago Manual of Style
Suggestions to Authors of the Reports of the United States Geological Survey

Created: ( Wednesday, 06 April 2011 15:55 )
Last Updated: ( Monday, 27 June 2011 07:56 )