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Can a chatbot hallucinate?

Q: Why do some writers say ChatGPT is “hallucinating” when it makes stuff up (e.g., recites lines of prose supposedly by Mark Twain that he never wrote, as the NY Times reports). To me, the chatbot is lying, not hallucinating.

A: When a chatbot simply makes something up, the untruth is a “hallucination” in the lingo of artificial intelligence.

As The Times reports in a Jan. 10, 2023 article, a chatbot may tell you that “Mark Twain’s Celebrated Jumping Frog of Calaveras County could not only jump but talk. A.I. researchers call this generation of untruths ‘hallucination.’ ”

But is such an untruth a mistake—the machine’s best guess at something it doesn’t know—or is it a lie? Shouldn’t the machine admit that it doesn’t know?

Your question, as you can see, is pretty complicated. We don’t pretend to be experts on the ethical implications of chatbots, but we can throw some light on the history of “hallucinate” and “hallucination.”

And as it turns out, the new senses of the words in artificial intelligence aren’t as new as you think. They reflect the words’ original meanings in the 16th and 17th centuries, when to “hallucinate” was to be in error, to be deceived, or to lie, and a “hallucination” was caused by error or deception.

Both verb and noun came into English from Latin, according to the Oxford English Dictionary. They can be traced to the Latin verb alucinari (“to wander in mind, talk idly, prate,” the dictionary says, though some other sources suggest an earlier antecedent, the Greek αλύειν (alyein, to be confused or distraught).

The verb entered English first, in the mid-1500s, when to “hallucinate” meant to be mistaken or misled. The OED defines it more broadly this way: “To be deceived, suffer illusion, entertain false notions, blunder, mistake.”

The earliest example we’ve found is from a poem entitled “An Artificiall Apologie” (1540), a satirical broadside by “the ryght redolent & rotounde rethorician R. Smyth.”

The author says he has included annotations so that “the imprudent lector shulde not tytubate [stumble, go astray] or hallucinate in the labyrinthes of this lucubratiuncle [scholarly writing].”

Smyth deliberately peppered his verse with obscure, unusual, and exaggeratedly learned words for humorous effect. And “hallucinate” must have been extremely obscure at the time, since the next example we’ve found in the sense of “mistake” appeared almost a century later:

“Sir Hu[m]frey with all his diuinitie [divinity] had not iudgement to distinguish, he proueth nothing but doth onelie hallucinate betweene trueth and falsehood.”  From The VVhetstone of Reproofe (1632), by a church sexton identifying himself as “T.T.”

(Incidentally, the “VV” in the title above represents “UU,” for the letter “W,” an early usage that we discussed in a  recent post on the blog.)

The OED’s earliest citations for the verb “hallucinate” are from the mid-17th century, in passages accusing seers and healers of being mistaken. Here’s the first one, which we’ve expanded:

“If Prognosticators have so often hallucinated (or deceiving, been deceived) about naturall effects” (Πυς-μαντια: The Mag-astro-mancer, 1652, an examination of astrology and witchcraft by a Puritan clergyman, John Gaule). The first element in the Greek title is ersatz Greek, but the second, –μαντια, refers to divination.

As for that other early meaning of “hallucinate” (to lie), it lasted for only a few decades before falling out of use.

The OED labels this sense “rare” and “obsolete,” adding that it was “apparently” found only in dictionaries or glossaries of the early 17th century. Oxford cites examples from two early dictionaries,  which define “hallucinate” as “to deceive, or blind” (1604) and “to deceive” (1623).

In searching old databases, however, we’ve found an example in an anonymous political tract that clearly refers to a falsehood, not a mistake: “No sure, in thist you hallucinate verie palpably and groasly” (Bad English, yet Not Scotch, published in London in 1648).

The noun “hallucination” in its early sense (a false or mistaken idea) is still known today, though that’s no longer the principal meaning in modern English.

Oxford defines this sense as “the mental condition of being deceived or mistaken, or of entertaining unfounded notions,” as well as “an idea or belief to which nothing real corresponds; an illusion.”

The earliest example we’ve found is from a religious treatise of the 1630s, aimed at those who are industrious in their material lives but inattentive to God:

“millio[n]s of people shall be in hell, who according to their hallucination, their misdeeming [mistaking], their alas! misseconceit, thought that they were not idle.” (The Ransome of Time Being Captive, John Hawkins’s 1634 translation from the Spanish of Andreas de Soto.)

And here’s the OED’s first example for this sense of the noun (a mistaken belief): “Notions … arising from the deceptions and hallucinations of Sense” (Select Discourses, by the philosopher John Smith, probably written around 1650 and published in 1660).

Around this time, the mid-17th century, the spookier and more familiar meanings of “hallucinate” and “hallucination” emerged. These senses involve not just erroneous notions, but deranged or supernatural experiences—seeing or hearing things that aren’t real.

The noun in this sense is defined in the OED as a term in “Pathology and Psychology” for “the apparent perception (usually by sight or hearing) of an external object when no such object is actually present.” The dictionary notes that it’s “distinguished from illusion in the strict sense, as not necessarily involving a false belief.”

Here’s Oxford’s earliest recorded example: “If vision be abolished it is called cæcitas, or blindnesse, if depraved and receive its objects erroneously, Hallucination” (Pseudodoxia Epidemica, 1646, by the physician Sir Thomas Browne).

The verb “hallucinate” in the modern, deranged sense took longer to enter the mainstream. The pathological meaning of the verb wasn’t recorded, as far as we can tell, until the end of the 19th century.

The earliest example we’ve found is in a doctor’s report on a patient in a mental hospital, published in a South Carolina newspaper:

“He is very obedient and courteous, but continues to hallucinate, often stating that the spirit voices keep him awake at night” (Keowee Courier, May, 21, 1919).

And this is the OED’s earliest citation: “A man hallucinated that the clothes of the girls ‘flew off them’ ” (The Creative Mind, 1930, by the British psychologist Charles Edward Spearman).

That meaning of “hallucinate,” plus the corresponding sense of “hallucination,” are the ones chiefly recognized today in standard dictionaries. Some, however, add that “hallucination” less commonly can mean an unfounded or mistaken belief.

No standard dictionary has yet recognized the new deceptive chatbot sense of “hallucinate” and “hallucination.” But it has become established in the Artificial Intelligence industry, where unreliable data is a problem.

In the words of Vilius Petkauskas, a senior journalist at Cybernews, “chatbots hallucinating convincing fakes can lead to anything from misunderstandings to misinformation” (March 6, 2023).

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