I've caught myself writing (typing) "possible" instead of "possibly" a few times over the past few days, while I do intend to write "possibly". Only upon rereading the sentence I notice my mistake.

It is not a typo. I am able to touch-type on a qwerty layout on which 'e' and 'y' are both written using a different hand, and different fingers. The keys are two keys apart from each other.

A simple google search for "psychology writing wrong words" didn't show up any immediate relevant results. I did read about a Freudian Slip, but it seems highly unlikely I would make such a mistake due to an "unconscious ('dynamically repressed'), subdued, wish, conflict, or train of thought".

Is there any psychological phenomenon explaining why I would make such an error?

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    $\begingroup$ These (non-academic) articles cover some of why your brain fails to pick up those errors and cite some good sources: marianneworley.com/2011/06/02/… wired.com/wiredscience/2010/10/fingers-know-typos $\endgroup$ – Ben Brocka Jan 23 '12 at 20:09
  • $\begingroup$ On a personal note: I have had this happen 3 times in the last 48 hours. I think sleep deprivation is the contributing factor but it is scary. Examples: I wrote 'Brad' instead of 'Brian'. I wrote 'thing' instead of 'think' and I wrote 'ass' instead of 'all'. I also confused tax day April 15 with April 13 and struggled to recall my work cellphone. I feel like I am losing it. I have multiple degrees and am fairly put together so this has been really disturbing. $\endgroup$ – user4773 Apr 10 '14 at 4:00
  • $\begingroup$ I have had the same problem lately, mixing up simple words like their, there and they're for example. I know exactly which should be used where so that is not the issue with me either. Also when I read over what I've written my mistake jumps out at me and I can't believe I have made such a basic error. This is only a problem I've encountered in the last few months. I am wondering whether it could be the beginning of Alzheimer's, as it does sit in my family. From what I understand Alzheimer's begins in the basal ganglia which is the same part of the brain used for writing. $\endgroup$ – user4886 Apr 24 '14 at 13:42
  • $\begingroup$ I do this too, and it drives me bonkers. It is even worse for me because when I do it, it's not with a related work. I type a different word starting with the same letter and usually with the same number of characters: "instead" instead of "inside" was the newest example in an email to my wife just today. And then there's times I just miss a word all together. $\endgroup$ – scott.korin May 15 '14 at 15:47
  • $\begingroup$ I do make a lot of errors too when typing especially when I am in a hurry and not paying much attention. But when I write with a pen as opposed to typing, I hardly make such errors. May be my poor typing skills have something to do with it. $\endgroup$ – user10686 Feb 9 '16 at 1:29

The speech error taxonomy on Wikipedia that Jeromy Anglim links to in his answer is pretty comprehensive. If you're interested in learning more, I would suggest reading some articles by Gary Dell (e.g., Dell, 1986). He is, in my opinion, the expert in this domain. He has used neural networks to explain speech errors of different types.

When mentally planning the next word in a sentence, we must choose the appropriate lemma. By selecting the units in a neural network that correspond to a certain lemma, it spreads activation to the corresponding morphemes, which in turn spreads activation to its corresponding phonemes. When the activation of a phoneme unit exceeds a certain threshold, it is selected for utterance (e.g., spreads activation to the motor units that allow us to speak).

However, this model is susceptible to retroactive and proactive interference: if we have just spoken another word that requires a different morpheme, its activation may exceed that of the target morpheme because of (for instance) undue attention or neural noise.

The same model can predict typographic errors as well: phonemes spread activation to orthographic units, which spread activation to the proper motor units which control our fingers.

Interestingly, speech errors rarely violate the rules of syntax, morphology, or phonology (even though they may make little sense semantically). Psycholinguists can use this fact in order to infer the structure of linguistic rules without having direct, conscious access to them.

Dell (1986). A Spreading-Activation Theory of Retrieval in Sentence Production. Psych Review, 93, 283-321. Retrieved from

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  • $\begingroup$ I know the model of Dell, but I've never heard of the link with finger movements. Can you provide an article about that? $\endgroup$ – Mien Feb 4 '12 at 0:17
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    $\begingroup$ @Mien I don't know of a paper that specifically looks at that aspect (though there may be one-- I haven't looked). However, 1) if you're willing to accept that Dell's model affects your tongue and jaw muscles, it seems a small leap that it would affect your fingers as well; 2) Botvinick & Plaut (2004) present a popular connectionist model of motor action selection that references Dell several times-- probably a good place to start. $\endgroup$ – Jeff Feb 14 '12 at 1:40
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    $\begingroup$ I was just rereading this answer, given that another user posted the same question. After a second read I notice that I actually do not make the speech error of saying "possible" instead of "possibly". Wouldn't that invalidate this answer? (hence the unaccept) $\endgroup$ – Steven Jeuris Sep 12 '13 at 21:40
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    $\begingroup$ I don't believe this answers the question. For example, why do I accidentally type "it's" when I know it should be "its"? There is nothing in phonemes or morphemes that would cause that kind of mistake. $\endgroup$ – mawcsco Sep 12 '13 at 21:45

A few thoughts (this is not my area):

  • This article on speech errors on Wikipedia is informative. The article provides a review types of speech errors. The classification of speech errors is presumably similar to writing errors.
  • What I take from the article, and other research on errors, is that there is plenty of structure to errors. I think an information processing perspective would be more helpful in explaining writing errors than a Freudian perspective.
  • Taking an information processing perspective on your specific example ("possible" versus "possibly"), it makes sense that these words could be confused on the basis of their semantic and spelling similarity.
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As an addition to Jeromy's answer, I would like to point out that I sometimes think of them as muscle memory flaws. I have no evidence to back this up, but I'll explain my reasoning. The suffix 'ble' is quite common in English language, so when you type the 'bl' for ('bly' in 'possibly'), without thinking you add the 'e' instead of the 'y', because your fingers are used to the pattern of 'ble'. Of course you can type the (perhaps) less common 'bly' but then you'll need a bit more attention, to inhibit the 'bly'.

Does this sound reasonable?

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    $\begingroup$ Yes it does, and I appreciate your input, but I can't up vote this because this site expects "good, well supported answers". $\endgroup$ – Steven Jeuris Jan 23 '12 at 18:54
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    $\begingroup$ I was just rereading the answer, and actually this might be more plausible. As far as I know I don't make the speech error of saying 'possible' when I meant 'possibly', so even though if "phonemes spread activation to orthographic units" that would not lead to me typing it wrong. $\endgroup$ – Steven Jeuris Sep 12 '13 at 21:28

John Fields in his 2003 psycholinguistics textbooks says:

Note that the there -> their example is not a spelling error - the writer is fully aware of the difference between the two forms; but, under the pressure of writing, one form (often the more frequent one) is substituted for the other.

And he is correct about the relative corpus frequency of those words (google ngram below):

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If we apply the same theory to possibly -> possible, the difference in relative frequency is even greater:

enter image description here

This idea of higher-frequency word "takeover" (my term) is backed up by some more empirical research, but contradicted by others:

With regard to lexical properties, some studies of spontaneous speech errors (del Viso et al., 1991; Kelly, 1986) as well as errors arising in cases of acquired spoken language deficits (Blanken, 1990, 1998; Gagnon et al., 1997; Martin, Dell, Saffran & Schwartz, 1994) have reported that error responses are biased to be higher in frequency than their targets. However, a number of other studies have found no such effect (spontaneous errors: Harley & MacAndrew, 2001; Vitevitch, 1997; experimentally induced errors: Dell, 1990; aphasic errors in spoken production: Best, 1996; written production: Romani, Olson, Ward, & Ercolani, 2002).

Another interesting issue is that written errors seem to cross syntactic category boundaries more often than speech errors:

In addition, a large number of studies have reported very high rates of syntactic category preservation in spoken errors produced both spontaneously (Abd-El-Jawad & Abu-Salim, 1987; Arnaud, 1999; Berg, 1992; del Viso et al., 1991; Fay & Cutler, 1977; Fromkin, 1971; Garrett 1975, 1980; Harley, 1990; Harley & MacAndrew, 2001; Leuninger & Keller, 1994; Nooteboom, 1969; Rossi & Defare, 1995; Silverberg, 1998; Stemberger, 1985) as well as subsequent to neurological impairment (Best, 1996; Berg, 1992; Blanken, 1990; Dell et al., 1997; Gagnon et al. 1997; Martin et al., 1994; but see Blanken, 1998). Some studies of written errors have reported that the tendency to preserve grammatical category is weaker in written than in spoken production—and is perhaps non-significant (spontaneous: Hotopf, 1980; aphasic errors: Romani et al. 2002).

Perhaps this partly explains why people don't seem to make this possibly -> possible substitution in speech. (One is an adjective, the other an adverb.)

And as far terminology goes, this is sometimes called an "atomic typo", at least among writers:

Another kind of typo—informally called an "atomic typo"—is a typo that happens to result in a correctly spelled word that is different from the intended one, and since it is spelled correctly, the spellchecker cannot find the mistake. Examples include "unclear" instead of "nuclear", "you" instead of "your", "Sudan" instead of "sedan" (leading to a diplomatic incident in 2005 between Sudan and the United States regarding a nuclear test code-named Sedan), "Untied States" instead of "United States", and "the" instead of "they". The ["atomic typo"] term was used at least as early as 1995 by Robert Terry.

And regarding speech errors (which a lot of answers here point to). Depending whether you are willing to call typos spelling errors or not (Field won't), this is or isn't a (written) malapropism. There's not complete consensus whether accidental pronunciations (or typos) that produce word substitions should be called that:

Definitions differ somewhat in terms of the cause of the error. Some scholars include only errors that result from a temporary failure to produce the word which the speaker intended. Such errors are sometimes called "Fay-Cutler malapropism", after David Fay and Anne Cutler, who described the occurrence of such errors in ordinary speech. Most definitions, however, include any actual word that is wrongly or accidentally used in place of a similar sounding, correct word. This broader definition is sometimes called "classical malapropism", or simply "malapropism".

And I'm not entirely convinced Wikipedia has this issue right

Under the name of malapropisms, Fay and Cutler (1977) have examined a variety of speech error. However, malapropisms in the classical sense are not speech errors: they are what the speaker intended to say and would be willing to repeat. This paper analyzes 158 classical malapropisms in English. Though some probably result from imperfect learning, most represent errors of storage in the mental lexicon. Statistical assessment of the examples indicates that they most resemble the ‘tip of the tongue” phenomenon, rather than slips of the ear or malapropisms in the Fay/Cutler sense.

Anyway, what seems to be a reasonable conclusion here is that "atomic typos" include the written equivalent of Fay-Cutler malapropisms.

The UPenn Language Log discusses a recent example of the latter, which is a bit long to reproduce here with the accompanying discussion in full. But the point there is that "committed of a crime":

is an "error" because if you showed the writer the sentence and invited him to review it, he would (I surmise) say "oops" and correct "committed" to "convicted". In contrast, a (classical) malapropism, as deployed by one of the Mrs. Malaprops of the world, is a case where the speaker or writer has entered the wrong word into their mental lexical, and would not be aware that they're making a mistake even if they had the opportunity to review what they said or wrote.

The error in this case is "phonological" because committed and convicted are both three-syllable words with medial stress, whose initial and final syllables are almost the same. And the error is "semantic" because someone is convicted of having committed an offense, so that there's a close relationship in the psychological space of meanings.

Why do I think that this case is a Fay-Cutler malapropism, i.e. a (written form of a) speech error?

For one thing, if we look at a somewhat edited collection, namely the COCA corpus of 425 million words of recent American English, the pattern "committed of a crime" gets no hits, while "convicted of a crime" gets 99, and "committed a crime" gets 236. [...]

the substitution has the general lineaments of a Fay-Cutler-type speech error: same number of syllables, same stress pattern, same lexical category, same first and last syllables.

So we can also call possibly -> possible "a typo with the general lineaments of a Fay-Cutler-type speech error". Ha ha. Linguists need more roundabout terminology. Actually not all the criteria are met: in particular, it's not the same lexical category in the case of possibly -> possible, but rather adverb -> adjective. I don't know if Fay & Clutler would have allowed for this.

This how they actually defined their notion of malapropism

First, the erroneous intrusion is a real word-not the intended word, of course, but not a meaningless string of phonemes either. Second, the target and error seem to be unrelated in meaning. Finally, there is a close relation between the pronunciation of the target and the pronunciation of the error.

So possibly -> possible doesn't quite fit that definition because the words are semantically related. It goes to show how difficult it is to come up with a good categorization of errors.

And since (rereading your question) you think the word "typo" does not apply to this; linguists use "slip of the keyboard". These include two sub-categories (cf. Field, p. 70)

  • motor errors, where there is a failure in the signal that the brain sends to the hand or in the contact between hand and keyboard
  • lexical errors, where the wrong written form has been selected

You seem to think that "typo" only describes the first sub-category. But the Wikipedia definition of typo excludes spelling errors (that are a result of ignorance). And since your [lexical] error is not a result of ignorance, it's not excluded, so it is a typo.

What you probably mean to say is that it is a "nonspecified substitution". That means that neither key adjacency nor left/right mirroring were the cause. These two are common causes of "motor" (in the sense of Field) substitutions in typing.

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