To define Webster 1913 a little further and to present some note worthy etymology in addition to charlie_b 's very helpful and informative write up. Plagiarism is a form of academic dishonesty; it is the academic equivalent of larceny. Sibling to plagiarism, is forgery and both are defined in terms of not being genuine, but being presented to the reader as genuine, and so presented with the intention to deceive. Reputedly and apparently, qualities or character has to do with authorship, or source of issue. Comparatively, the difference between plagiarism and forgery is that a person plagiarizes when he attempts to fob off another's work as his own, however he forges when he tries to pass off his own work as another's. Both are prima facie morally wrong.

With the advent of the internet there have been a number of issues brought to the forefront. "Houses of Cheat," as some web sites have been referred to by academic institutions, have popped up like weeds selling or giving away papers on almost any subject. Many students are tempted to "Download their Workload" either because they are unsuspecting freshmen or simply lack integrity. Most colleges and universities have adopted very strict policies for dealing with plagiarism considering it a major crime that earns the plagiarizer a failing grade in the course. In many cases the school expels the student and the act of plagiarism is made a matter of record on the student's transcript.

There is very little philosophical literature on plagiarism but what creates the issues surrounding what is plagiarism and what is not, is the fact that many times there is a legitimate influence. Simply put, most work is affected by others, with all kinds of results in their work. Hence plagiarism is typically reserved, for the conspicuously offensive lifting of material in an unchanged or only slightly changed form and its presentation as the plagiarist's own work. If in doubt I highly recommend reading
Plagiarism: What It is and How to Recognize and Avoid It at
http://www.indiana.edu/~wts/wts/plagiarism.html

It gives some very excellent examples vs. non examples of plagiarism under the sub heading How to Recognize Unacceptable and Acceptable Paraphrases

Merriam Webster defines the transitive sense as, "to steal and pass off (the ideas or words of another) as one's own: use (another's production) without crediting the source." and the intransitive sense as, "to commit literary theft: present as new and original an idea or product derived from an existing source." Webster dates it earliest known usages in print as 1716 and notes that the related noun for this word is plagiarizer.

The Barnhart Concise Dictionary of Etymology relates a little etymology," plagiarism comes from the English noun plagiary, meaning “literary thief.” What’s more, the English plagiary was borrowed from the French plagiere, which was borrowed from the Latin plagi_rius [sic – ed.] meaning “kidnaper, seducer, plunderer or literary thief.” " (1621)

More history of the word. It was used during the seventeenth century from an obsolete noun plagiary meaning kidnapper or a kidnapping, theft or a thief of ideas. Plaga is the Latin word that indicated a snare or hunting net for capturing animals. Plagium was also used to denote the netting of game, as well as, for the crime of kidnapping children to be sold into slavery. A plagerous was a kidnapper. By the first century AD, the same word was used to refer to a literary thief or plagiarist. From this sense, plagiarism came to describe the practice of stealing the ideas or words of others and passing them off as one's own. kthejoker reading about Martial's epigrams says, "(T)the most interesting thing to me was that he called his writing his "slaves." He saw his work as putting food on his table, and this was kidnapping his workers to work for someone else." Etymologist Alan Rosiene tells an interesting story of how the subject of literary property in ancient Rome evolved from hunter to criminal and finally into metaphor from the Greek poet M. Valerius Martialis:

    "As states, it is M. Valerius Martialis who first transferred the concept of "kidnapping" to plagiarism of literary works. Counting varies in different editions of Martial's epigrams...

    Apparently, the legal term for one who stole a child or slave was 'plagium,' and the person so doing was known as plagiarius. Martial's epigram (I.52) transfers the use of the word to the theft (or borrowing, to mitigate the matter) of another's words and seems to be the first such use (though the argument about filching others' words already had a long history by Martial's day (in Greece as well as Rome), with varied opinions about the rightfulness or wrongness of such acts.

    (An) edition of Martial's first book, from (a London edition, 1980) does not much differ on this point... According to (the reference) plagiarius never refers to a "plagiarist" in Classical Latin, except for the metaphorical use in Martial 1.52.9. Lorenzo Valla...picks up Martial's metaphor to refer to someone who was using his work. The use, an extension of a legal metaphor in Martial picked up by Lorenzo Valla, caught on.

    Interesting (to note) that Gk. *plagiazô,* from *plagios,* has the meaning "turn aside, pervert, use tortuous methods" in the Septuagint and Philo .... and *plagios* itself is said to come from *plazô* .....which Aristarchus took for a form of *plêssô* ...I suppose. *plagios* already has the sense "morally crooked" in the 5th cent B.C." [typography standardized – ed.]

In 1779 writers were poking fun at plagiarism with a played called The Critic where there appeared a disputable and highly questionable character created by Richard Brinsley Sheridan who took the name from the word ‘plagiarism’ called Sir Fretful Plagiary. It is a lively parody on the problems of producing a play, with Sir Plagiary as a burlesqued persona of Richard Cumberland, a well-known author of a number of very sentimental and successful comedies who also translated Greek plays such as Aristophanes.

You might be interested to know that there has been a plagiarist detector invented by Walter Stewart and Ned Feder at the National Institutes of Health in Bethesda, Maryland. The instrument has an optical scanner that inputs the text under scrutiny into a computer that is programmed to group it into lines of thirty characters that overlap and then compared against material related to the same subject matter. Highlighting in boldfaced type occurs when there are any exact matches. The device has been used in a number of situations with success. The inventors of the system 'have learned ... that plagiarism is rare; and that people who copy do so from obscure places and chiefly from dead authors' (International Herald Tribune, 8 Jan. 1992).

Sources:

etymology:
www.geocities.com/etymonline/p6etym.htm

Index of messages from Classics.Log9506b:
omega.cohums.ohio-state.edu:8080/hyper-lists/ classics-l/listserve_archives/log95/9506b/

Merriam-Webster Online Dictionary, copyright 1999 Merriam-Webster, Inc

xrefer:
http://w1.xrefer.com/entry/443391

This node has been edited by Cletus the Foetus.