as a unit:Readers expect a unit of discourse to be a story about whoever shows up first."Bees disperse pollen"and "Pollen is dispersed by bees"are two different but equally respectable sentences about the same facts.The first tells us something about bees;the second tells us something about pollen.The passivity of the second sentence does not by itself impair its quality;in fact,"Pollen is dispersed by bees"is the superior sentence if it appears in a paragraph that intends to tell us a continuing story about pollen.Pollen's story at that moment is a passive one. Readers also expect the material occupying the topic position to provide them with linkage (looking backward)and context (looking forward).The information in the topic position prepares the reader for upcoming material by connecting it backward to the previous discussion.Although linkage and context can derive from several sources,they stem primarily from material that the reader has already encountered within this particular piece of discourse.We refer to this familiar,previously introduced material as"old information."Conversely,material making its first appearance in a discourse is"new information."When new information is important enough to receive emphasis,it functions best in the stress position. When old information consistently arrives in the topic position,it helps readers to construct the logical flow of the argument:It focuses attention on one particular strand of the discussion,both harkening backward and leaning forward.In contrast,if the topic position is constantly occupied by material that fails to establish linkage and context,readers will have difficulty perceiving both the connection to the previous sentence and the projected role of the new sentence in the development of the paragraph as a whole Here is a second example of scientific prose that we shall attempt to improve in subsequent discussion: Large earthquakes along a given fault segment do not occur at random intervals because it takes time to accumulate the strain energy for the rupture.The rates at which tectonic plates move and accumulate strain at their boundaries are approximately uniform.Therefore,in first approximation, one may expect that large ruptures of the same fault segment will occur at approximately constant time intervals.If subsequent main shocks have different amounts of slip across the fault,then the recurrence time may vary,and the basic idea of periodic mainshocks must be modified.For great plate boundary ruptures the length and slip often vary by a factor of 2.Along the southern segment of the San Andreas fault the recurrence interval is 145 years with variations of several decades. The smaller the standard deviation of the average recurrence interval,the more specific could be the long term prediction of a future mainshock. This is the kind of passage that in subtle ways can make readers feel badly about themselves.The individual sentences give the impression of being intelligently fashioned:They are not especially long or convoluted;their vocabulary is appropriately professional but not beyond the ken of educated general readers;and they are free of grammatical and dictional errors.On first reading,however,many of us arrive at the paragraph's end without a clear sense of where we have been or where we are going.When that happens,we tend to berate ourselves for not having paid close enough attention.In reality,the fault lies not with us,but with the author. We can distill the problem by looking closely at the information in each sentence's topic position: Large earthquakes The ratesas a unit: Readers expect a unit of discourse to be a story about whoever shows up first. "Bees disperse pollen" and "Pollen is dispersed by bees" are two different but equally respectable sentences about the same facts. The first tells us something about bees; the second tells us something about pollen. The passivity of the second sentence does not by itself impair its quality; in fact, "Pollen is dispersed by bees" is the superior sentence if it appears in a paragraph that intends to tell us a continuing story about pollen. Pollen’s story at that moment is a passive one. Readers also expect the material occupying the topic position to provide them with linkage (looking backward) and context (looking forward). The information in the topic position prepares the reader for upcoming material by connecting it backward to the previous discussion. Although linkage and context can derive from several sources, they stem primarily from material that the reader has already encountered within this particular piece of discourse. We refer to this familiar, previously introduced material as "old information." Conversely, material making its first appearance in a discourse is "new information." When new information is important enough to receive emphasis, it functions best in the stress position. When old information consistently arrives in the topic position, it helps readers to construct the logical flow of the argument: It focuses attention on one particular strand of the discussion, both harkening backward and leaning forward. In contrast, if the topic position is constantly occupied by material that fails to establish linkage and context, readers will have difficulty perceiving both the connection to the previous sentence and the projected role of the new sentence in the development of the paragraph as a whole. Here is a second example of scientific prose that we shall attempt to improve in subsequent discussion: Large earthquakes along a given fault segment do not occur at random intervals because it takes time to accumulate the strain energy for the rupture. The rates at which tectonic plates move and accumulate strain at their boundaries are approximately uniform. Therefore, in first approximation, one may expect that large ruptures of the same fault segment will occur at approximately constant time intervals. If subsequent main shocks have different amounts of slip across the fault, then the recurrence time may vary, and the basic idea of periodic mainshocks must be modified. For great plate boundary ruptures the length and slip often vary by a factor of 2. Along the southern segment of the San Andreas fault the recurrence interval is 145 years with variations of several decades. The smaller the standard deviation of the average recurrence interval, the more specific could be the long term prediction of a future mainshock. This is the kind of passage that in subtle ways can make readers feel badly about themselves. The individual sentences give the impression of being intelligently fashioned: They are not especially long or convoluted; their vocabulary is appropriately professional but not beyond the ken of educated general readers; and they are free of grammatical and dictional errors. On first reading, however, many of us arrive at the paragraph’s end without a clear sense of where we have been or where we are going. When that happens, we tend to berate ourselves for not having paid close enough attention. In reality, the fault lies not with us, but with the author. We can distill the problem by looking closely at the information in each sentence’s topic position: Large earthquakes The rates