Dissertation: The logical structure underlying temporal references in natural language

Bruce, B. C. (1971). The logical structure underlying temporal references in natural language. Ph.D. dissertation, The University of Texas at Austin, Computer Sciences Department. [Note: The archival file is very large; here’s the content in a smaller file size.]

Committee: Norman M. Martin (Co-Chair), Robert F. Simmons (Co-Chair), Michael Richter, Terrence W. Pratt

From the Introduction:

Temporal reference in natural language include tenses and other time relations, references to specific times, and a variety of phrases such as “present”, “later”, “when”, “how often”, and “never”. Their high frequency of occurrence reflects the importance of time to the users of natural language. Although the structure underlying temporal references may appear complicated, it is a working assumption of this thesis that a sound logical explanation of its characteristics can be made.

The frequent use of temporal references makes a correct exhibition of their underlying structure vital to a full understanding of natural language. Such an understanding is important in teaching and translating, indeed in all uses of natural languages. In addition, understanding language better should aid in the design of computer programs which process natural languages.

Chapter 2 of this thesis surveys some relevant work on temporal references, both to show what has been done and to show the scope of the problem. Despite the divergence in terminology and viewpoint, a unified theory can be derived which relates and extends the previous work.

The new theory is presented in Chapter 3. It is a formal system which models the intuitive meaning of tenses, time relations, and other references to the time of events. The system precisely defines and shows the interrelationships of concepts which are often only vaguely defined. By its generality and its logical foundation, the system is able to serve as a skeleton for further studies of time in language.

To illustrate some of the features of the system a question answering computer system, called Chronos, was written which accepts information in the form of tensed sentences and answers questions about the time of events. This program is discussed in Chapter 4.

Chapter 5 discusses a problem which arises when we consider assigning truth values to statements about events occurring at times other than the present. The problem is to define a logic for unknown outcomes which retains the two valued technologies. A logic is presented which has two kinds of implication: a material implication for which all the classical tautologies hold, and a strict implication defined in terms of logical necessity. The strict implication fragment of this logic is shown to be slightly stronger than the Lewis (1959) system S5, although it avoids many of the so-called paradoxes of material implication. The logic of Chapter 5 is a useful extension of the system for tenses (Chapter 3) to situations in which future (and perhaps past) events may have the truth value “unknown”.

Chapter 6 is a discussion section which evaluates the tense system, the logic for unknown outcomes, and the program Chronos. Several possibilities for extending the thesis are discussed.

Chapter Title Page
1 Introduction 1
2 Background 4
3 A Model for Temporal References in Natural Language 37
4 Chronos 54
5 A Logic for Unknown Outcomes 70
6 Discussion 85
7 References 89

Chapters 3 and 4 were combined, revised, and published as

Bruce, B. C. (1972). A model for temporal references and its application in a question answering program. Artificial Intelligence: An International Journal, 3, 1-26.

Chapter 5 was revised and published as

Bruce, B. C. (1976). A logic for unknown outcomes. Notre Dame Journal of Formal Logic, 17, 542-550. Also as Report No. CBM-TM-35. New Brunswick, NJ: Rutgers University Computer Science Department.

Summer jobs

This is a summary of some of the summer and part-time jobs I had before going to graduate school at the University of Texas.

  • Summer, 1968 (age 21). Research assistant at the Institute for the Study of Cognitive Systems at Texas Christian University. The Institute, directed by Selby Evans, was interested in pattern recognition by computer. I wrote a program to produce systematic distortions in black and white images so that we could assess the effectiveness of different pattern detection algorithms (see “Production and control of visual pattern variability by computer”). For example, we could then say that algorithm X could detect a pattern which had been distorted 30% along a particular dimension, but not 40%. The distortions included various versions or rotating, stretching, flipping, or just adding random noise.
  • Rice University, Psychology

    Rice University, Psychology

    School year, 1966-67 and 1967-68. Psychology department research assistant at Rice University. I helped set up experiments on behavioral conditioning in rats and learned a little about electrical circuit design.

  • ice-bag-2Summer, 1967 (age 20). Research assistant at the Public Health Service Clinical Research Center in Fort Worth. This was one of two Federal research centers, the other being in Lexington, Kentucky. The Center housed both VA psychiatric patients and criminal addicts. My job was to review case files looking for patterns in the lives of addicts, such as those related to early drug use and job history.I learned a lot about the importance of community in shaping young people’s lives, and how hard it was to change individual behavior when it was nearly impossible to secure a job or to find meaningful opportunities away from a drug culture.
  • Earlier that summer I had a brief job working in an ice house, primarily carrying bags of ice from a conveyor belt to a truck, because there was no machine to do that.
  • orderly2School year, 1965-66. Mail room worker at Rice University. I briefly got to drive the little mail truck until one of the other workers got drunk and smashed it up.
  • Summer, 1965 and 1966 (ages 18 and 19). Orderly at All Saints Hospital in Fort Worth. I learned how to perform various kinds of enemas and catheterizations, work with patients in the psychiatric ward, apply orthopedic weights for patients whose limbs were lifted by ropes and pulleys, and do various other procedures that a teenager with no experience would not be allowed to do today. My co-workers came from all over Fort Worth, representing a variety of backgrounds. They helped open up my world.I read later that Nietzsche was a hospital orderly during the Franco-Prussian War, which influenced his views of life and death, including the development of the idea of Will to Power.200px-apollo_program_insignia
  • School year, 1964-65. Experimental subject for the NASA Apollo program. I was one of three “astronauts” in a simulated three-day mission to outer space. We ate dehydrated space food and carried out mostly boring and repetitive tasks. We each had 11 electrodes pasted on to our bodies to monitor EEG, ECG, and vital signs. One outcome of the study was to learn that paste-on electrodes don’t work after about 2 1/2 days, because the hair grows back.
  • fwzooSummer, 1964 (age 17). Concession stand worker at the Fort Worth Zoo. We sold soft drinks, fries, and BBQ sandwiches. Each morning we had to fill out a squirrel damage report detailing any destruction of supplies due to squirrels and other zoo residents. This started with things like “3 bags of corn chips had chew holes in them.” But we were called in when it began to say, “4 large drinks, 2 BBQ sandwiches, 1 without onions, 3 orders of fries.”My friends Leslie, Ben, John, Hull, and others worked there, too, so we had lots of time to talk about books, life, and our futures. We’d go bowling at lunchtime, sometimes managing to get to the bowling alley, bowl three games, and still get back before the half hour lunch break was over.scuba-diving-03
  • Summer, 1963 (age 16). Researcher for Colonial Cafeterias. My friend John Horan and I used contest entry forms to develop a primitive geographic information system (GIS) representing the source of patrons of the cafeteria. We also scouted out competing cafeterias to assess the level of current and potential business in different areas of town.
  • Also, that summer, a job cleaning public swimming pools using scuba equipment in order to stay under the water longer.
  • ivory-piano-keysSummer, 1962 (age 15). Piano repair at the Bruce Piano Company.
  • Summer and part-time, 1959-63 (ages 12 to 17). Various yard work jobs–mowing, edging, clearing brush, raking leaves, etc.; newspaper delivery