Part I    Introduction14
fei75766_ch01_001-018.indd 14  02/06/20 10:41 AMadministration, andpsychotherapy. Most ofthetheories discussed inthisbook have
hadsome influence inareas beyond psychology. Forexample, Freud’s theory has
prompted research onrecovered memories, atopic veryimportant tothelegalpro-
fession. Also, CarlJung’s theory isofgreat interest tomany theologians andhas
captured theimagination ofpopular writers suchasJoseph Campbell andothers. 
Similarly, theideas ofAlfred Adler, ErikErikson, B.F.Skinner, Abraham Maslow, 
CarlRogers, Rollo May, andother personality theorists havesparked interest and
action inabroad range ofscholarly fields.
Is Internally Consistent
Auseful theory need notbeconsistent withother theories, butitmust beconsistent 
withitself. Aninternally consistent theory isonewhose components arelogically 
compatible. Itslimitations ofscope arecarefully defined anditdoesnotoffer explana -
tions thatliebeyond thatscope. Also, aninternally consistent theory useslanguage 
inaconsistent manner; thatis,itdoesnotusethesame termtomean twodifferent 
things, nordoesitusetwoseparate terms torefertothesame concept.
Agood theory willuseconcepts andterms thathavebeen clearly andopera -
tionally defined. Anoperational definition isonethatdefines units interms ofobserv -
ableevents orbehaviors thatcanbemeasured. Forexample, anextravert canbe
operationally defined asanyperson whoattains apredetermined score onaparticular 
personality inventory.
Is Parsimonious
When twotheories areequal intheirability togenerate research, befalsified, give
meaning todata, guide thepractitioner, andbeself-consistent, thesimpler oneis
preferred. Thisisthelawofparsimony .Infact,twotheories arenever exactly equal 
inthese other abilities, butingeneral, simple, straightforward theories aremore use-
fulthanonesthatbogdown under theweight ofcomplicated concepts andesoteric 
language.
 Dimensions for a Concept  
of Humanity
Personality theories differ on basic issues concerning the nature of humanity. 
Each personality theory reflects its author’s assumptions about humanity. 
These assumptions rest on several broad dimensions that separate the vari -
ous personality theorists. We use six of these dimensions as a framework for 
viewing each theorist’s concept of humanity.
The first dimension is determinism versus free choice.  Are people’s 
behaviors determined by forces over which they have no control, or can people 
choose to be what they wish to be? Can behavior be partially free and partially Final PDF to printer