If you are looking at the occupations listed in census records, you 
might be interested in a study that sorted them into larger economic 
categories, such as skilled or unskilled blue collar workers, or low or 
high-status white collar workers.  See Thernstrom, referenced below.  
The classification of occupations into socio-economic ranks that 
Thernstrom developed was also used by V. Cowin in her study of 
Pittsburgh and to by M. Weber is his study of Parren, Pennsylvania.  I 
have found it useful in my on-going study of historic communities around 
Pittsburgh.  but I found that not all the occupations I find were 
included in Thernstrom's original classification, so I have had to make 
some guesses of my own about where additional occupations would fit into 
his ranking system.
In my case, I included "gentleman" with "none," "retired," and blank 
entires for occupation, in an "Other" category and did not try to rank it.
References:
Stephen Thernstrom, The Other Bostonians: Poverty and Progress in the 
Maerican Metropolis 1880-1970.  Harvard University Press, 1973.
Verna L. Cowin, Pittsburgh Archaeological Resources & National Register 
Survey.  Carnegie Museum of Natural History, Pennsylvania Historical and 
Museum Commission, and Pittsburgh Department of City Planning.  Report 
on file at the Pennsylvania Historical and Museum Commission, 
Harrisburg, PA.
Michael P. Wber, Social Change in an Industrial Town: Patterns of 
Progress in Warren, Pennsylvania, from Civil War to World War I.  
Pennsylvania State University Press, Univeristy Park, PA.

Melissa Diamanti
Archaeological & Historical Consultants, Inc.

Kent Taylor wrote:

>In looking through censuses, directories, and other historic documents, I
>sometimes come across types of occupations that are not easily defined by
>our modern standards.  Does anyone have a list of occupations for the entire
>historic period and exactly how they were defined during their period of
>use?  For example, the occupation of "gentleman."  How was that defined? 
>Was he a retired person?
>Thanks in advance,
>Kent Taylor
>