To be able to assess the content, organization, and continuity of your writing, you need to be able to identify topics and the focus of those topics. A topic is whatever the segment of text is "about." Topics can occur at all levels: sentence, paragraph, section, chapter, parts of books, and of course books. Topics are the building blocks of your communication. The better you can visualize them, the better you can write and revise. This is especially true at the paragraph and section levels of a document.
That process of capturing the topic and topic focus of each paragraph can be called topic analysis. And it's not necessarily a simple thing to do. But that's the topic of this chapter.
Identifying topics at the sentence level is straightforward—or at least way more so than at the paragraph level. Quite often the topic is at the beginning of the sentence, as the subject. But not always. Consider these examples:
| Individual sentences | Topics |
| Voyager 1 could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan. | Voyager 1 |
| The winter solstice occurs (around December 21st) when the angle reaches its maximimum value (about 113.5 degrees). | winter solstice |
| The main advantage of the Mark I was that it was fully automatic—it didn't need any human intervention once it started. | Mark I |
| In 2000, NASA cancelled the Pluto Kuiper Express mission, citing increasing costs and launch vehicle delays. | Pluto Kuiper Express |
Even though advantage comes before it, the topic of the sentence 3 is Mark I; advantage is the topic focus. Sentence 4 presents a challenge: is the topic NASA or Pluto Kuiper Express? Hard to say, isn't it? You can only know by looking at the paragraph context in which this sentence occurs—and you'll see that context in the following.
As mentioned at the beginning, the real value of topic analysis is at the paragraph level and beyond. When you look at a page of, say, five paragraphs, it's not necessarily an easy thing to think about how it is organized. It's much easier if you can make a mental map or outline of the sequence of topics. You shift from looking at 250 words to looking at 15 words—maybe 3 per paragraph. Consider this paragraph and its main topic and its subtopics:
| Paragraph | Topic | Subtopic |
| Pluto presents significant challenges for spacecraft because of its small mass and great distance from Earth. | Pluto missions | challenges |
| Voyager 1 could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan. | Pluto missions | Voyager 1 |
| Voyager 2 never had a plausible trajectory for reaching Pluto. | Pluto missions | Voyager 2 |
| In 2000, NASA cancelled the Pluto Kuiper Express mission, citing increasing costs and launch vehicle delays. | Pluto missions | Pluto Kuiper Express |
| The first spacecraft to visit Pluto will be NASA's New Horizons, launched on January 19, 2006. | Pluto missions | New Horizons |
However, with the preceding analysis, you've got more to do. This topic analysis won't help much in evaluation the organization of the paragraph. You need to define topics and subtopics in terms of the overall focus of the paragraph. The subtopics, in this example, are the topics of all the sentences following the first sentence where the main topic occurs.
Ask yourself what sentence 2 through 5 have in common. They are each about a space mission to or near Pluto. Not all of the mission were to Pluto; one just csme close. Thus the common subtopic could be defined as, let's say, mission, with the "to or near" part understood:
| Paragraph | Topic | Subtopic |
| Pluto presents significant challenges for spacecraft because of its small mass and great distance from Earth. | Pluto missions | mission challenges |
| Voyager 1 could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan. | Pluto missions | mission |
| Voyager 2 never had a plausible trajectory for reaching Pluto. | Pluto missions | mission |
| In 2000, NASA cancelled the Pluto Kuiper Express mission, citing increasing costs and launch vehicle delays. | Pluto missions | mission |
| The first spacecraft to visit Pluto will be NASA's New Horizons, launched on January 19, 2006. | Pluto missions | mission |
But wait a minute! Subtopics are not always identical to each other. Consider this example:
| Paragraph | Topic | Subtopic |
| Mars is the fourth planet from the Sun in our solar system and is named after Mars, the Roman god of war. | Mars | location, name |
| Mars is also known as the "Red Planet" due to its reddish appearance when seen from Earth. | Mars | appearance |
| The prefix areo-, from the Greek god of war, Ares, refers to Mars in the same way geo- refers to Earth. | Mars | name |
| Mars has two moons, Phobos and Deimos, which are small and oddly shaped. | Mars | moons |
While the main topic remains Mars throughout, the subtopics shift from location and name to name to appearance back to name then to moons. Is this okay? Certainly. It's very common for a paragraph to discuss a range of subtopics related to the main topic.
Notice that one of the benefits of topic analysis of paragraphs is that you can spot sequencing (organization) problems. The name of Mars is discussed in sentence 1 and sentence 3. Why not keep the naming discussion in one spot rather than allowing appearance to interrupt it?
Should we give these different kinds of subtopic sequences a name? Is there a reall difference? In the Pluto paragraph, sentence 2 through 5 each focused on a different space mission in some way involving Pluto. In the Mars paragraph, the subtopics are fundamentally different: name, location, appearance, moons. However, it's difficult coming up with terms that don't sound negative. Static? Consistent? Unified? Various? Random? Varying? (Both are subcategories of coordinate structure.)
The topics of the paragraphs you've seen to this point have been obvious. You may have become so accustomed to seeing planets as topics you might mistake this next one:
The surface of Mars is thought to be primarily composed of basalt, based upon the Martian meteorite collection and orbital observations. There is some evidence that a portion of the Martian surface might be more silica-rich than typical basalt, perhaps similar to andesitic stones on Earth, though these observations may also be explained by silica glass. Much of the surface is deeply covered by iron oxide dust as fine as talcum powder. There is conclusive evidence that on the surface of Mars liquid water existed at one time. Key discoveries leading to this conclusion include the detection of various minerals such as hematite and goethite which usually only form in the presence of water.
Here, the main topic is not Mars but the surface of Mars. Every sentence focuses on some aspect of the Martian surface. In fact, the topic word occurs in all but one of the sentences, and it is certainly implicit in the sentence where it is excluded. How is the paragraph different from the missions-to-Pluto paragraph? There, we defined the main topic as missions to or near Pluto—or was it Pluto? Each of the following sentences had as its subtopic mission (singular). Here, we could define the main topic as Mars or the Martian surface, with each of the subtopics being surface aspect.
The most important part of a solar heating system is the solar collector whose main function is to heat water to be used in space heating. There are various types of collectors. However, the flat-plate collector is the most common and the focus of the following discussion. A flat-plate collector consists of a box-shaped black plate absorber covered by one or more transparent layers of glass or plastic with the sides and the bottom of the box insulated. These layers of glass or plastic have an intervening air space that produces the heat-trapping effect. Water is heated as it circulates through or below the absorber component, which is heated by solar radiation.
The development of the transistor goes back to the nineteenth century. Germanium and silicon, along with a number of other crystalline materials, are semiconductors, so-called because they neither conduct electricity well, like most metals, nor block it effectively, as do insulators such as glass or rubber. Back in 1874 a German scientist named Ferdinand Braun identified a surprising trait of these on-the-fence substances: Current tends to flow through a semiconductor crystal in only one direction. This phenomenon, called rectification, soon proved valuable in wireless telegraphy, the first form of radio communication. When electromagnetic radio waves traveling through the atmosphere strike an aerial, they generate an alternating (two-way) electric current. However, earphones or a speaker must be powered by direct (one-way) current. Methods for making the conversion, or rectification, in wireless receivers existed in the closing years of the 19th century, but they were crude. In 1899 Braun patented a superior detector consisting of a semiconductor crystal touched by a single metal wire, affectionately called a "cat's whisker." His device was popular with radio hobbyists for decades, but it was erratic and required much trial-and-error adjustment.
The preceding has mentioned topic focus. While a topic is whatever the sentence or paragraph is about, the topic focus is what the sentence or paragraph says about that topic. Consider these examples at the sentence level:
| Individual sentences | Topic | Topic Focus |
| Voyager 1 could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan. | Voyager 1 | change of mission |
| The winter solstice occurs (around December 21st) when the angle reaches its maximimum value (about 113.5 degrees). | winter solstice | occurrence, definition |
| The main advantage of the Mark I was that it was fully automatic—it didn't need any human intervention once it started. | Mark I | main advantage |
| In 2000, NASA cancelled the Pluto Kuiper Express mission, citing increasing costs and launch vehicle delays. | Pluto Kuiper Express | reasons for cancellation |
As you can see, defining the topic focus is trickier than it is for topics. While a paragraph topic can be something definitive like Pluto, you can phrase the topic focus in any number of ways. As long as your phrase captures the topic focus, you're on the right track.
| Paragraph—main topic: Pluto, topic focus: missions to or near | Subtopic | Subtopic focus |
| Pluto presents significant challenges for spacecraft because of its small mass and great distance from Earth. | —— | challenges to missions |
| Voyager 1 could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan. | mission | change of plan |
| Voyager 2 never had a plausible trajectory for reaching Pluto. | mission | not planned |
| In 2000, NASA cancelled the Pluto Kuiper Express mission, citing increasing costs and launch vehicle delays. | mission | reasons for cancellation |
| The first spacecraft to visit Pluto will be NASA's New Horizons, launched on January 19, 2006. | mission | planned mission |
Notice a bit more about what's going on here. Instead of using spacecraft in the topic focus for sentence 1, we used missions. It's for the same reason we reduced all of the subtopics to mission. Your goal is to see the common thread or theme—yes, topic, subtopic, even focus—running through the paragraph. You can see that the individual subtopic focus items don't have as much in common. The common focus seems to be something like what happened or will happen to these missions involving Pluto.
You might have noticed that sentence 1 states a thesis that the rest of the sentences do not support. Sentence 1 cites small mass and great distance from Earth as the problem with missions of Pluto. Sentence 4 does only a distant flyby of that thesis. While some readers might object to this under-developed thesis, it doesn't seem like a problem here in a single paragraph. As readers, we'd have every reason to object if this were the thesis of the whole document and the document never showed how it was true.
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