Definition

          Four techniques are of special importance in technical writing: definition, description of a mechanism, description of a process, and classification. These techniques are not types of reports and it is important to remember that these techniques usually appear in a single report. It would be exceptional to find an entire report, even a short one, containing only one of these techniques. For example, two or more techniques might be closely interwoven as a writer described the design, construction, and operation of a mechanism. The intermingling of these techniques, however, does not alter the basic principles of their use. These techniques can be studied most effectively by taking one technique at a time.
         The treatment of these techniques will stress the practical rather than the theoretical, particularly in the subjects on definition and classification.
         In technology, words have precise, specific meanings; therefore there is a need for defining a technical term clearly. The extent to which a term should be defined or the length of a definition depends on the writer's purpose and the knowledge level of the reader.
         Before going to the problem of "how to define", it is better to "think about what should be defined first." It is not possible of course, to set up an absolute list of terms and ideas that would require definition, not even for a specific body of readers, but it is possible and desirable to clarify the point of view from which the problem of definition should be attacked.
         The relationships of words to the ideas and things for which they stand can become very complex. However, there is a simple and helpful way of classifying words, as they will appear to your reader. The words will fall into one of the following categories:
1. Familiar words for familiar things
2. Familiar words for unfamiliar things
3. Unfamiliar words for familiar things
4. Unfamiliar words for unfamiliar things
1. Familiar words for Familiar things. The only observation that need be made about the first category is that familiar words for familiar things are fine; they should be used whenever possible. To the extent that they can be used, definition is unnecessary. Nothing is ever gained by using, just for the impressiveness, words that may puzzle the reader.
2. Familiar words for unfamiliar things. The words in this second category present a rather special problem to the technical writer. These are the everyday, simple words that have special meanings in science and technology. Most of them may be classed as "shop talk," or language characteristic of a given occupation. Because they are a part (often a very colorful part) of the language of a specialized field, it is easy to forget that they may not be a part of the vocabulary of the reader, at any rate not in the special sense in which they are used. Consider a term like "quench". Everyone knows this word in the familiar sense, but not everyone knows that in the metallurgical sense it means the dipping of heated steel into water, oil, or other bath, to impart necessary hardness.
         Every field of engineering and science has a great many of these simple words that have been given specialized meanings.
Examine the following list:
Bastard  - A course-cut file but not as rough as a first-cut.
Bite - Trade term for etching on metal plate.
Bed - The part of the lathe which supports the headstock, tailstock, and carriage.
Doctor - Local term for an adjuster or adapter that allows chucks from one lathe to be used on another. The term "dutchman" is sometimes used in this way.
Dog - The carrier of a lathe. One of the jaws of the chuck.
Land - Space between flutes or grooves in drill, taps, reamers,
and other tools.
Nose - The business end of tools or things. The threaded end of a lathe or milling-machine spindle, or the end of a hog-nose drill or similar tool.
Cheater - An extension on a pipe wrench.
Dirty - To make ink darker.
         The reader may not confuse the everyday meaning of such terms with the technical sense they have in a particular report, but there is not much doubt that when encountering a term of this sort, the reader, unless a specialist in the field being discussed, will initially wrongly identify the word according to its everyday meaning. In any event, the writer must be alert to the need for defining such terms.
3. Unfamiliar words for Familiar things. We condemned writers who prefer big and pretentious words for referents with which their readers are familiar. Such a practice should always be condemned if a simple, familiar term exists which means the same thing. But an unfamiliar word for a familiar thing may be used if there does not exist any simple, familiar term for it. Both convenience and accuracy justify it. Suppose an electrical engineer was writing about special tactical electronic equipment making use of direct wave transmission. It is not likely that he would be satisfied to use the phrase "short wave" when dealing specifically with, say, the 300- to 3000- megacycle band. A more precise phrase is "ultrahigh frequency" (UHF). Your solution is simple: you use the convenient term but you define it.
         You will have to judge whether your subject matter demands the use of such terms and whether they are familiar to your readers. If they are needed, or if they are justifiably convenient, and you decide that your readers do not know them, you should define them.
4. Unfamiliar words for unfamiliar things. This category embraces most of those words that are commonly thought of as "technical" terms. They are the specialized terms of professional groups; big, formidable looking (to the non-specialist), they are more often than not of Greek or Latin origin. Terms like "dielectric," "hydrosol," "impedance" are typical.
          With these facts in mind about what to define, we can more intelligently consider the problem of how to define.
Methods of Definition
         In so far as it is possible to use simple, familiar terminology, the problem of definition may be avoided entirely. In other words, the best solution to the problem of definition is to avoid the need for it. When it is necessary, however, there are two methods or techniques that may be employed. The first may be described as informal; the second, as formal. The second takes two forms: the sentence definition and the extended or amplified definition. Each of these techniques has its own special usefulness.
Informal
         Essentially, informal definition is the substitution of a familiar word or phrase for the familiar term used. It is therefore a technique to be employed only when you are reasonably certain that it is the term alone and not the referent which is unfamiliar to the reader.
         Instead of a single-word substitution, sometimes a phrase, clause, or even a sentence may be used in informal definition. Such kinds of definition have general facts and they are worthwhile to be noted and these are:
First, they are partial, not complete definitions. But such illustrations are enough in a discussion where thorough understanding of the terms is not necessary and the writer merely wants to identify the term with the reader's experience.
Second, informal definitions are particularly adapted for use in the text of a discussion. Because of their brevity and informality, they can be fitted smoothly into a discussion without appearing to be serious interruptions.
Third, when the informal definition reaches sentence length, it may not be greatly different from the formal sentence definition. It lacks the emphasis, and usually the completeness however which may be required if a term defines an idea or a thing that is of critical importance in a discussion. In short, if one wants to make certain that the reader understands a term and that the term is important enough to focus special attention on it, he will find the formal sentence definition, and perhaps the amplified definition or article of definition, more effective.
Formal Sentence Definition
         The informal definition does not require the application of an unchanging, rigid formula; rather, it is an "in other words" technique - the sort of thing we all do frequently in conversation to make ourselves clear. In formal definition, however, it is different. A logically dictated, equation-like statement is always called for, a statement composed of three principal parts for which there are universally accepted names. These are the species, the genus, and the differentia.
The species is the subject of the definition, or the term to be defined.
The genus is the family or class to which the species belongs.
The differentia is that part of the statement in which the particular species' distinguishing traits, qualities, and so forth are pointed out so that it is set apart from the other species comprising the genus.
Species
= Genus
+ Differentia
Brazing    
is a welding process                        
wherein the filler metal is a non-ferrous metal or alloy whose melting point is higher than 1000F but lower than that of the metals alloys to be joined.
1.The term - the word or phrase to be defined
2.The class or genus - the specie or family to which the term belongs
3.The differentia - that part of the definition which states the distinctive characteristics of the term which distinguishes it from other members of the same class.
Defined as a process, then, formal definition involves two steps:
1. Identifying the species as a member of a family or class
2. Differentiating the species from other members of the same class.
          The first step in the process of formal definition is that of identifying a thing as a member of a genus, or class. It is important to choose a genus that will limit the meaning of the species and give as much information as possible. In other words, the genus should be made to do its share of the work of defining. It wouldn't help much, for instance, if a micrometer caliper is a "thing" or "device." Generally speaking, the more informative the genus is made, the less one will have to say in the differentia. The more specific one can be in the genus, the less he has to say in the differentia.
          Care must be taken in carrying out the second step of the process of formulating a sentence definition. Here the important point is to see that the differentia actually differentiates - singles out the specific differences of the species. A statement which attempts to differentiate a species must be examined critically to see if the definition is applicable solely to the species that is defined. If the statement is true of something else, it may be sure that the differentia is not sufficiently precise. One way to test a statement is to turn it around and see whether the species is the only term described by the genus and differentia.
Example:
          "A C-shaped gauge in which the gap between the measuring faces is minutely adjustable by means of a screw whose end forms one face is a ." "Micrometer caliper" fills the blank, and if the definition is correct, it is the only term that accurately fills the blank. An accurate limiting genus coupled with a precisely accurate differentia will always ensure a good definition.
          Practice in the writing of such formal definitions is good mental discipline as well as excellent training in conciseness and care in the use of words. However, extreme care must be taken in order to guard against certain faults that can impair their usefulness. Here are some pointers which must be followed when formulating formal definitions:
1. Define a word in simpler and more familiar terms. The purpose of definition is to clarify, not to confuse. A definition more difficult than the term being defined is useless.
ex:
Not this : An emulsion is a fluid consisting of a microscopically heterogeneous mixture of two normally immiscible liquid phases, in which one liquid forms minute droplets suspended in the other liquid.
Better: An emulsion is a fluid consisting of two microscopically different liquids which are insoluble with each other, wherein, one liquid forms very tiny droplets suspended in the other liquid.
2. Practice grammatical parallelism when defining a term. If the term is a noun, a gerund, or an infinitive, the class should be the same. Avoid defining with "is when," "is where," and "is what." Is, being a linking verb, must be followed by the same type of construction that precedes it and an adverb clause cannot serve as a predicate nominative.
ex:
Not this: To oscillate is moving in a regular manner from side to side or back and forth.
Better: To oscillate is to move in a regular manner from side to side or back and forth.
3. Avoid circular definition which means the explanation of a term using the word itself or any of the derivatives. Nothing is achieved when a term is defined by mere repetition.
ex :
Not this : Engineering is the art and sciences taken up by persons to become engineers.
Better: Engineering is the professional art of directing the great sources of power in nature (matter and energy) for the benefit of man.
4. Do not put the term to be defined in too broad or too narrow a class.
ex :
Too broad: A riffle is a weapon . . . (knives, ice picks, swords, etc. are also weapons.)
Too narrow: A rifle is a gun . . . (pistols, revolvers, etc. are also guns)
Better: A riffle is a firearm with spiral grooves inside its barrel to impart rotary motion to its projectile or bullet and thus render its flight more accurate.
          The extended definition is developed using any or a combination of the following methods:
1. Details
         A term can be clarified by the addition of related or supporting particulars. To define a mechanism, a vivid description of its various parts will enable the reader to "see" it.
2. examples of instances
         General statements particularly abstract definitions are made more concrete when illustrations are cited.
3. analogy, contrast or comparison
         Analogy cites similarities. The reader is made to understand an unfamiliar object or idea by comparing it with another object or idea more familiar to the reader. Using contrast, the differences of both objects are cited in order to make the idea clear. Comparison combines the two methods of analogy and contrast (pointing out similarities and differences).
4. word derivation
         Extended definitions may be revealing and interesting because they explain the origin of the term or the idea. Definitions such as these are seldom logically adequate but they are often extremely useful illustrations for clarification.
The one sentence definition usually serves as the topic sentence in an extended, amplified, or expanded definition.
Analogy
The human eye is the organ of sight or vision. Its parts are very similar to the parts of the camera. The zone sensible to light in the eye is called the retina and in the camera, the photographic film. The body of the eye and the camera is called the darkroom. The glass in our eye is the lens which focuses the image. The adjustable hole; for the lighting the eye is called the iris and in the camera, the diaphragm. Besides these structural characteristics, the eye, like the camera, receives the images from the outside world in an inverted position.
Contrast
         A laser is a powerful beam of coherent light, the rays of which stay parallel over vast distances. The laser light beam is entirely different from the beam produced by all other light sources. In the first place, the ideal laser beam consists of light on a single wavelength. A beam of light from other sources contains a range of colors and is not concentrated in one specific color. The second difference between a laser beam and an ordinary light beam is that the light waves that form the laser beam are all in phase; that is, the crests of the waves all occur together. This kind of light is called coherent light. Other light sources generate waves that are out of phase with each other. As a result, troughs may occur at the same time as crests, producing a much less powerful beam. Such a beam diverges if some form of focusing is not used. An ideal laser beam, however, will not diverge.
Comparison
          There are two measuring devices which are both used to measure short distances accurately, the vernier caliper and the micrometer caliper. The vernier caliper is a semiprecision-measuring tool used to measure short distances accurately to hundredths of a centimeter, whereas the micrometer caliper is a precision measuring instrument used to measure very short distances accurately to thousandths of a centimeter. Both the vernier and the micrometer calipers have two scales. The vernier caliper has the fixed scale and the sliding or the vernier scale. In the Metric System, the fixed scale is calibrated in millimeters and the vernier scale in tenths of a millimeter. If the fixed scale reads 2 centimeters and 3 millimeters, this means 0.07 cm. Adding the two readings 2.3 + 0.07 = 2.37 - the actual reading. The two scales of the micrometer caliper are the horizontal and the vertical. The horizontal gives the readings in hundredths of millimeters or thousandths of a centimeter. The actual reading is equal to the sum of the readings which will be in thousandths of a centimeter. While the vernier caliper can be calibrated in both the Metric and English systems, the micrometer caliper can be calibrated in the Metric system only.
Word Derivation
          Geometry is a very old science. The word geometry is derived from the two Greek words, geos meaning "earth" and metron meaning,”measure"; hence literally, geometry means "earth measure." It is supposed to have had its beginning with the land surveying by the priests of Egypt. The Nile River periodically overflowed its banks carrying away landmarks in its valley, and by altering its course, increased or decreased the taxable value of the adjoining lands. This necessitated frequent measurements to re-establish vanishing landmarks and to determine not only the position of property but also its extent. Recognizing the merits of having a system in such a branch of knowledge, the Greeks sought to transform and develop the art of mensuration which they learned from the Egyptians into a science. At present, the word geometry has a broader and deeper meaning than it had when it was first adopted. It is that branch of mathematics which deals with the relations among and measurements of lines, angles, surfaces, and solids.