Definitions of the "T-unit"

Detail from Madonna with saints and  members of the Pesaro family 1519-26  TITIAN (approx. 1495-1576)

     In 1965, Kellogg Hunt's Grammatical Structures Written at Three Grade Levels established the "T-unit" as the fundamental yardstick for measuring natural syntactic development. Researchers had long been seeking some way of accurately measuring the obvious increase in length and complexity of children's sentences as they grow older, but all attempts had failed. The apparently obvious method -- counting the average number of words per sentence -- fails because very young children write very long sentences composed of several compounded main clauses. In hindsight, Hunt's solution appears simple -- he counted the average number of words per main clause. Because of differences in the definition of "main clause," he called his basic unit of measurement a "T-Unit," which stood for "minimally terminable unit." 
     A "T-Unit," for Hunt,  is essentially a main clause defined as including all subordinate clauses and other constructions that go with it. Hunt's work was so convincing that almost every research project that followed it has used his concept of  the "T-unit." Far too often, however, researchers have whimsically redefined the T-unit such that the yardstick is not a good yardstick. As a result, not only is comparison between studies almost impossible, but the studies themselves are often incomprehensible. Starting from Hunt's original study, this essay will examine the redefinitions in some of the major studies. The differences in definitions should explain why any serious study should be accompanied by complete transcripts of the students' writing.

1965
Kellogg Hunt,  Grammatical Structures Written at Three Grade Levels

     Hunt's explanation of the "T-unit" is so crucial that it needs to be given in full:

3-8. A More Promising Index 
      The increase in mean clause length and the increase in the number of subordinate clauses add up to something worth noting. If it is true that (1) the average main clause written by successively older students has more subordinate clauses attached to it, and if, in addition, (2) those clauses are longer, then the total length of such a unit would of course increase as a result of the two subsidiary kinds of lengthening. This unit whose total length is being discussed contains, to repeat, one main clause with all the subordinate clauses attached to it. The number of subordinate clauses can, of course, be none.
      The length of such a unit might turn out to be a good index of maturity. It might turn out to be an even better index than the two subsidiary factors because of the fact that an individual who was high in subordination index but low in clause length (or the reverse) would have those opposite tendencies moderated by this combining index. 
      A whole piece of writing could be sliced up into units of this sort, just as a rib pork roast is sliced off into chops. The person slicing need only be careful to cut where the joints come instead of cutting into a chunk of solid bone. There should be no trouble deciding whether an expression, if it is intelligible at all, goes with the preceding main clause or the following. An and between two main clauses would always go with the second clause, beginning it just as coordinating conjunctions so often begin the sentences of mature writers. A student's failure to put in periods where he should would not interfere with the slicing process unless the passage already was an unintelligible garble. 
      Here is a sample to be sliced up. It is printed just as the fourth grader wrote it, except that the spelling is corrected. It is a whole theme, punctuated as one sentence, 68 words long. This one fourth grade sentence is four times as long as the average twelfth grade sentence.

 I like the movie we saw about Moby Dick the white whale the captain said if you can kill the white whale Moby Dick I will give this gold to the one that can do it and it is worth sixteen dollars they tried and tried but while they were trying they killed a whale and used the oil for the lamps they almost caught the white whale

      That same theme sliced off into these unnamed units appears below. A capital letter now begins each unit and a period ends each one. A slant line indicates the beginning of each new clause. One unit begins with an and, and another with a but. Each unit is grammatically capable of being considered a sentence. In fact, these units are the shortest grammatically allowable sentences into which the theme could be segmented. If it were segmented into units any shorter, some fragment would be created. 

1. I like the movie / we saw about Moby Dick, the white whale. 
2. The captain said / if you can kill the white whale, Moby Dick, / I will give this gold to the one / that can do it. 
3. And it is worth sixteen dollars. 
4. They tried and tried. 
5.  But / while they were trying / they killed a whale and used the oil for the lamps. 
6. They almost caught the white whale. 

     As segmented above, several units contain only a single clause -- a main clause, of course -- like a simple sentence. There are several multi-clause units like complex sentences. In fact, the second unit is rather intricate, for within the main clause is embedded a noun clause and within it is both an adverbial if clause and an adjective clause. There are no units like compound sentences or compound-complex sentences, for such units must be cut into two or more parts so that each will contain only one main clause. 
      These units need a name. It would be simplest to call them "minimal sentences." However, the word "sentence" already has so many different meanings that misunderstanding would be certain to result. The word "sentence" has troubles enough already. A fresh, neutral sounding name would be better. These units might be christened "minimal terminable units," since they would be minimal as to length, and each would be grammatically capable of being terminated with a capital letter and a period. For short, the "minimal terminable unit" might be nicknamed a "T-unit." One would hesitate to use both initials and let it be nicknamed an "M T unit." So "T-unit" will be the name used for it in this investigation. 
      As a potential index of maturity, the unit has the advantage of preserving all the subordination achieved by a student, and all of his coordination between words and phrases and subordinate clauses. 
      Slicing a theme into these units does destroy the student's coordination between main clauses, or, more accurately, between T-units, as in numbers 3 and 5 in the theme above. But to do so is a gain rather than a loss, if one is searching for an index of maturity. For it has already been shown that certain fourth graders destroy the significance of sentence length by their tendency to string T-units together endlessly with and after and, forgetting to use periods. In fact, coordination with and between T-units is an index of immaturity significant for grade at the .01 level. So such destruction is merciful.
      In anticipation of actually testing out this index, we can see that it holds promise.
      Any two grammarians should be able to agree on an analysis, whether their denominations be transformational or structural or traditional. The investigators used in this study agreed without exception so long as they were confronted by well-formed sentences either declarative or interrogative. (20-22)

     "Before the writings could be analyzed, a small amount of extraneous matter had to be excluded. A piece of this extraneous matter, called a garble, was any group of words that could not be understood by the investigators. Here is a passage from the fourth grader who committed the most garbles. The garble is italicized. Where the investigators felt sure that a word was merely a wrong inflection, the correctly inflected form appears in parentheses.

     The man (men) burned the whales to make oil for the lamps in the town. And the man in the little boats and the white whale eat (ate) the boats up and the white whale went down and came up and eat (ate) The other up too and the rest came back to the ship.

. . .
     Two eighth graders and two twelfth graders each allowed one garble to stand unrevised and undeleted. Fourth graders committed more. One distinguished himself with fourteen garbles totaling 68 words. Another committed three totaling 10 words. Two others committed one each. All these fourth graders were boys. The nine girls committed no garbles.  (6)

The worst day I spent was when my momy told me my aunt died and had to go to school. 

    As noted previously Hunt's lack of a linguistic or psychological foundation for the "T-unit" led to its abuse. Researchers felt free to redefine it, often with little or no justification. But Hunt's work should be first base for anyone interested in natural syntactic development in school children.

1967
Roy O'Donnell, William J. Griffin, and Raymond C. Norris. Syntax of Kindergarten and Elementary School Children: A Transformational Analysis

     This study is more complicated than Hunt's in that it covers oral as well as written language. The researchers, however, adopted Hunt's definition of "T-unit" almost exactly. (33-34) Like Hunt, they also eliminated garbles from the word count,

but two special rules were adopted to make the count more uniform and meaningful. Contractions such as he'd and isn't were regarded as two words, and compound nouns (whether written solid or hyphenated in dictionaries) were given the count indicated by the number of bases involved. Thus "snowball" would be counted as two words. (33)

1976
Walter Loban's Language Development: Kindergarten through Grade Twelve

     One of the purposes of Loban's study was "[t]o examine the language development of the same group of children from age five until age eighteen." Covering both oral and written language, it is the most comprehensive, and probably the most sophisticated study that has ever been done on natural language development. It runs into problems with its "Elaboration Index Weights." Beyond the T-unit, Loban attempts to measure syntactic maturity by assigning point values to "language variables." An adjective is worth 1/2 point; parentheticals,, nominative absolutes,  prepositional phrases, modals, participles, gerunds, and infinitives are worth 2 points each;  objective complements and appositives get 3 each; a "First-order Infinitive Clause" (among others) earns 5 points. (17) These number values raise some very serious questions, but on the fundamental question, Loban's T-unit (which he calls a "communication unit") is Hunt's T-unit. (9)
     Like Hunt and O'Donnell, Loban attempts a statistical description of natural syntactic development, but he does not offer a psycholinguistic explanation of why such development occurs. (See "The Principles of Syntactic Development" in Chapter Four of  TGLA.)  He does, however, offer a very astute set of hypotheses on what else to look for as signs of maturity in syntactic development. (6-7). His study is also extremely valuable in that he divided the students into three groups (high, low, and random) based on a number of factors (21-23), and followed the development of each group.

1969
John C. Mellon's Transformational Sentence-Combining: A Method for Enhancing the Development of Syntactic Fluency in English Composition

      Mellon's study was an attempt to show that instruction in sentence-combining, together with instruction in transformational grammar, is more effective than traditional instruction in grammar. It predates publication of Loban's major study, but lists the work of Hunt and O'Donnell in the references. Interestingly, in his section on "Background Research," Mellon focuses on the Bateman-Zidonis study, rather than on the work of Hunt and O'Donnell. The Bateman-Zidonis study, which did not use the T-unit, was an attempt to compare  the teaching of grammar by using the Oregon Curriculum and teaching that used a more traditional approach. In this background section, Mellon's only mention of Hunt is to chide Bateman and Zidonis for not using the T-unit:

Bateman and Zidonis' scheme for computing structural complexity leaves much to be desired. Their use of the orthographic sentence ignores the findings of Hunt (1964), who shows that the independent clause is a more reliable unit. Apparently the experimenters wished to count coordinate conjunctions resulting in compound sentences, although the incidence of this structure is inversely proportionate to maturity (11-12)

His rules for T-unit segmentation are as follows:

He then explains that:

"These procedures are comparable to those employed by Hunt (1964). Item two, however, follows from the experimenter's view that logical conjunctions ('if,' 'although,' 'because,' 'so that,' etc. are T-unit connectors much like the coordinate conjunctions, in that both groups of words join independent clauses. Item seven also differs from Hunt's routine. It represents an attempt to discard clauses with repeating (thus elliptical and vacuous) predicate phrases, such as 'and so did John' or 'but neither could the man,' which otherwise would count as T-units." (42-43)

In the final analysis, however, it must be left to the reader himself to determine whether the enhanced growth experienced by the experimental subjects was indeed the direct result of transformational sentence-combining, as well as, incidentally, whether this growth represents a phenomenon which might just as accurately be labeled cognitive development. (72)

My family has seven people in it. First my dad then my mom then my oldest sister Cyndee and then me and Crystal,  Tara, and Amanda they're my youngest sisters.

The writing of the experimental group was inferior to that of the subjects who had studied conventional grammar, but indistinguishable from that of subjects who had studied no grammar but had received extra instruction in composition -- curious results indeed. (69)

the experimenter finds without exception that all widely used seventh grade texts are limited to these puerile sentence types. Apparently they are employed on the assumption that students of this age cannot learn to speak about the grammatical structure of more complex language. Not only is this untrue, it causes these students to experience and perhaps emulate sentences far below their attained level of syntactic fluency. Despite their manifest undesirability, these activities were chosen as the control treatment simply because they are conventional, established, and well-nigh universal in current seventh grade grammar programs." (38-39)

it may very well  be the case that conventional grammar study fails to promote growth of syntactic fluency not because of the usage practice which it features, but rather because of the hundreds of simply structured and altogether childish sentences which it employs for parsing exercises. As noted, this is the case with conventional textbooks generally, not merely with the one used in this experiment. Nor are the sentences featured in grades eight or nine very much more mature, although they include a wider range of construction types. If true, this observation raises serious doubts as to the manner in which linguistic study is currently being introduced to junior high school students in the vast majority of American schools, since it serves to impoverish rather than enrich the language environments of these students. (63)

     Having read Mellon's study, O'Hare decided to test pure sentence-combining against "traditional" instruction in grammar. Interestingly, he rejected most of Mellon's revisions of the definition:

     "Mellon counted clauses of condition, concession, reason, and purpose as separate T-units because he believed that logical conjunctions behave much like coordinate conjunctions. In addition, he discarded clauses with repeating predicate phrases because he claimed they were elliptical and therefore vacuous. This experimenter remained unconvinced by Mellon's reasoning in either case and, therefore, retained Hunt and O'Donnell's simpler and more convincing methodology." (48)

     "A very real difficulty arose when directly quoted discourse introduced by such an expression as 'He said . . .' was encountered. Mellon discarded the 'speaker tag.' This experimenter was unhappy with such a procedure because it soon became difficult to define the expression 'speaker tag.' There is no great loss when an expression like 'He said' is discarded. But what about the following example encountered in the analysis: 'Clutching the knife tightly in his bleeding hand, Joe painfully crawled towards the opening and said, 'I surrender'.' Exactly what is the speaker tag here? Technically speaking, it would include every word from 'Clutching' to 'said.' Surely this is not a two word T-unit with a sixteen-word speaker tag discarded!
     Hunt stated that 'there is some reason, then, to tabulate direct discourse along with noun clauses' (1965, p. 75). It would be easy to imagine directly quoted discourse consisting of a dozen sentences. Counting all of them as noun clauses would also be unsatisfactory. A compromise was reached by counting the first expression after 'He said' as a direct object, because it seemed to satisfy the minimally terminable requirement for a T-unit. For example, the following discourse --

Marsha said, 'I really like you, John. However, Clarence's father is a millionaire and I like the idea of Palm Beach.'

-- would have been segmented into three T-units -- between 'John' and 'However,' and between 'millionaire' and 'and.' The advantage of such a procedure was that it retained as much of the student's original writing as possible." (48)

     Without copies of what the students wrote, O'Hare's study is useless. His results were predictable without his study. He already knew that subordinate clauses begin to blossom in seventh grade, and that the blossoming of subordinate clauses produces a jump in the number of words per T-unit. He already know Mellon's conclusions. One must, therefore, question his selection of an experimental population: "The seventh grade was selected as the level on which to conduct this experiment simply because Mellon chose seventh graders." (37) O'Hare knew that he was going to get positive results, and he was almost certainly aware of the basic behaviorist theory of conditioning -- if one has students spend hours combining sentences into longer ones, longer ones will transfer to their writing -- until the conditioning wears off. One could, therefore, say that O'Hare used -- and abused -- Hunt's T-unit. The abuse is obvious in the title of the study. Whereas Mellon had used the word "enhancing," O'Hare used "improving." 
     Mellon, in his substudy, had found that the traditional grammar group did better in "overall quality." O'Hare conducted a much more limited study of overall quality, a study that is highly suspect. He concluded that "The experimental group wrote compositions that were judged to be significantly better, at the .001 level, in overall quality than those written by the control group." Because of this conclusion, we need to examine what he did in some detail.
     As in Mellon's study, errors in spelling and punctuation were corrected before the samples were evaluated for "quality." Then, thirty matched pairs of writing samples were assembled:

"it was decided that the system of forced choices between matched pairs of compositions would be utilized. Members of the control group were listed and numbered in ascending order of IQ for both boys and girls. A similar list was compiled for the experimental group. A subject was randomly chosen from the control group and a subject of the same sex and approximately equal IQ (within three of four IQ points) was chosen from the experimental group to make up a matched pair." (49)

"Of course, these evaluators had no knowledge of the nature of the present experiment. They were simply told to make a single judgment on the overall quality of the compositions in each pair, basing their decision on ideas, organization, style, vocabulary, and sentence structure." (50)

"during an initial practice period the evaluators were given two matched pairs of compositions, one pair exemplifying very good seventh grade writing and the other, the contrary. On the blackboard, from left to right, were written ideas, organization, style, vocabulary, and sentence structure. After each item was discussed in turn, the evaluators were asked to choose the composition they preferred, basing their judgments equally on all five factors. They were to indicate their preference by making a large check at the top of the preferred composition. Then there ensued a discussion of the relative merits of each of the paired compositions to establish some sort of general agreement concerning the five criterion factors. These five factors were left on the blackboard, and the evaluators were encouraged to glance there occasionally to ensure that they were taking all five into consideration in their judgments." (51)

     Because this study is sometimes cited to show that instruction in grammar is useless, the first thing that needs to be pointed out is that none of the researchers had a background in grammar or linguistics. They were administrators and teachers who were interested in the question of the effectiveness of formal instruction in grammar, and, because of chance and connections, they received a grant to do an extensive research project. Even a brief reading of their book, however, shows that their study went far beyond the question of grammar into questions of the teaching of literature, the effects of individual teachers on instruction, etc.  They deal with T-units in Chapter Eight, and their presentation is somewhat muddled:

"The segmentation of sentences into T-units followed the principles outlined by Hunt, with minor modifications based on Mellon. Thus:

(1) Each independent clause, plus its subordinate clauses and embeddings counted as one T-unit.

(2) The coordinating conjunctions 'and', 'but', 'yet', and 'so' (when it meant 'and so') were regarded as markers which separate adjacent T-units (except in cases where they separated two subordinate clauses).

(3) A clause was defined as an expression which contained a subject (or coordinated subjects) and a finite verb (or coordinated finite verbs).

(4) Sentence fragments which resulted from the omission of a single word were counted as T-units, with the missing word supplied.

(5) Interjections, parentheses, unintelligible words, vocatives and speaker tags in conversation were discarded.

Examples

(1) The policeman tracked down the thief. (1 T-unit)

(2) The policeman and the dog hunted and tracked down the thief. (1 T-unit)

(3) The policeman hunted through the thick bushes / and tracked down the thief. (2 T-units)

(4) The policeman, with his dog, hunted all night for the thief who had stolen and abandoned the new car / but did not catch him. (2 T-units) (74-75)

     Overall, this study addresses some interesting and important questions about the methods and procedures of conducting a research project designed to compare different methods of instruction. But the contradictions within their rules for defining T-units, and between the rules and the examples, make that aspect of this study meaningless.
 

     If it accomplished nothing else, the preceding discussion should have demonstrated the problems in defining the "T-unit" and the necessity of providing copies of the students' writing.  The research that appears on this site (which does include transcripts) is based on Hunt and O'Donnell's original definition of the "T-unit." That definition, however, is also the best definition of a "main clause," and thus I have used "main clause" in the research to "Keep It Simple." {Note that the final "S" in "KISS" does not imply that students are stupid; rather, it suggests that educators are because we give students numerous, often contradictory and complex definitions of terms and then wonder why the students can't understand and/or apply them.)
     Some adjustments have to be made, however, either because Hunt and O'Donnell did not address the questions, or because they lacked a psycholinguistic theory. These adjustments are:

Word Count: Words are counted as they are by a spelling checker. This means that hyphenated words and contractions count as one word. Word count raises some interesting questions, but O'Donnell's idea of counting "snowball" as two words seems unfounded. In KISS research, I am trying to explore how the brain chunks words (which represent concepts) in working memory. I doubt that anyone who mentions a snowball thinks of (and then chunks) the two separate concepts, "snow" and "ball." Hyphenated words raise an interesting question, but they are relatively rare, and, because transcripts are included, anyone who wants to can study the effect of counting them as two words instead of one. Contractions are counted as one word because, I would suggest, not all  transformations are equally important at all stages of language development.  In essence, by the time a person uses a contraction, I am suggesting that the underlying transformations have become almost automatic. (For more on this, see below.) Again, contractions are relatively rare, and anyone who wants to is welcome to explore the effect that counting them as two words would have. Transcripts are provided.

Garbles: As noted in the discussion of Hunt's work, garbles represent concepts in the writer's STM. They are therefore counted as words.

Fragments, Comma-splices, and Run-ons: Most of the researchers discarded fragments, but as with garbles, fragments represent concepts in STM. An orthographic fragment counts as a "T-unit." The assumption here is that an orthographic fragment is the result of an overloading of the writer's STM. The overloading causes the writer to put down an ending punctuation mark and begin a new "sentence." Counting fragments as "T-units is therefore consistent with the KISS psycholinguistic model. A student's average words per main clause (T-unit) is thus a reflection of the average number of words that the writer can process in STM before dumping to LTM. Discarding fragments would distort this number, probably upward. Attaching fragments to the appropriate main clause (as Mellon did) would also inflate this number.
     None of the researchers discussed above specifically looked at comma-splices and run ons, but the KISS research does. A problem arises here in that most main clause breaks have a double sign -- a closing punctuation mark followed by a capital latter. If either of these is present, and if the first word in the next main clause does not always begin with a capital (such as "I"), no error was counted. (The problem of interpreting and transcribing handwritten texts remains, but that is a different issue. Ideally students' handwritten texts should also be transcribed by someone who is competent but unfamiliar with the nature of the research project.)

Direct and Indirect Discourse: As noted above, O'Hare's decision about quoted discourse is probably the best. The first clause after something such as "He said ...." is counted as a noun clause, direct object. Subsequent direct object clauses (as in "He said he would go, but he would be back.") are counted as main clauses unless they are preceded by "that" ("He said he would go, but that he would be back."). The same rule applies to things such as "He thought ...."
     A problem that none of the researchers have addressed (because of the age groups that they are primarily working with?) is that of quotations and paraphrases in "research" papers. At this point in time, the KISS approach to this problem is to skip any main clause that includes such material.
 
 

     As Hunt noted, using his definition of the T-unit, "Any two grammarians should be able to agree on an analysis, whether their denominations be transformational or structural or traditional." Although he is right, and although the T-unit is the best basic yardstick of syntactic maturity, Hunt himself, plus all the other researchers looked for, and thought they found, additional measures (subordinate clauses, number of transformations, etc.). As noted above, however, there are substantial differences in the way that researchers have defined these measures. In addition, none of the research projects discussed above were based on a theory that could explain the nature of natural syntactic development. In effect, they were simply counting either constructions or transformations, as if all constructions or transformations of a given type are equal.
     Loban attempted to use a weighted scale, but even his scale overlooks the fact that some constructions (or transformations) may be more or less difficult in different stages of development. In some often cited research, for example, Carol Chomsky has pointed out that young children cannot distinguish between "eager to see" and "easy to see," but a year later -- without any specific instruction -- they have all mastered this difference. In terms of the KISS psycholinguistic model, this means that, confronted by one of these phrases, or in an attempt to generate one of them, the child has to devote a lot of the limited space in STM to it. As a result, there is less space left free in STM to handle the rest of a sentence. Chomsky's example also raises the question of the effect of vocabulary on T-unit length. Then too, numerous researchers have pointed out the effect of mode (narrative, expository, etc.) on T-unit length.
     Then there is the question of "formulas," first pointed out, to my knowledge, by O'Donnell (p.92), although neither he nor any of the other researchers deals with the question adequately. A "formula" is simply a grammatical string such as in "We have a cat named Sam." When a fourth grader writes this, do we say that she is using a participle (which Hunt considers to be a very advanced construction), or do we say that she has internalized the formula "_____ named _____." Clearly young children hear "_____ named _____" relatively often. Thus, if I understand him correctly, O'Donnell was suggesting that children learn formulas as vocabulary strings with slots for substitutions, as in "When daddy get(s) home." These are not true participles, subordinate clauses, etc., because the children have not mastered the underlying transformations which produce true participles, etc. Not all participles, in other words, are of equal value. And, in order to explore which are, and which are not, formulas, we need to see what the students' wrote (or said).

     Once again, Hunt's original definition of the "T-unit"  was such that  "Any two grammarians should be able to agree on an analysis, whether their denominations be transformational or structural or traditional," but we have seen how every researcher discussed above redefined it in some way that would affect the statistics. And once they go beyond the T-unit, things become a hundred times more complicated. The web was not available, of course, at the time that the studies discussed here were done. And reproducing transcripts of all the students' writing in the research reports themselves would have been economically impossible. But now we have the web. And any research project that wants to be considered seriously should provide (available on a web site) both copies and transcripts of all the students' work. Any project that doesn't will look as if it has something to hide.

See also the discussion of fragments in the Essay on Fourth Graders' Writing.

1. Mellon's study contains a number of unexplained redefinitions. Among other things, he counted the "Number of Relative Clauses: The number of unreduced relative clauses. Although traditionally labeled adverbial, clauses of time, place, and manner were counted as relative clauses whose head nouns had been deleted." No examples are given, and I simply do not understand this. How can "When we went to the store" in "When we went to the store, we bought candy," be considered as a relative clause whose head noun has been deleted?

2. I have been unable to find any research that demonstrates long-term effectiveness of sentence-combining exercises, and there are theoretical reasons for suggesting that some such exercises can be harmful, but that is a subject for a different essay. [Basically, sentence-combining exercises can be harmful when they violate the sequence of natural syntactic development by, for example, attempting to get fourth graders to embed appositives in their sentences.]