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The way we give information about a difference depends on a variety of factors
THE VARIETY OF DIFFERENCE LANGUAGE
As with similarities, discovering and naming differences is a major way of thinking analytically. It is important both in itself (see, for example, “compare and contrast” essays in 94. Essay Instruction Words) and for such academic activities as data analysis, classification, naming exceptions and describing advantages & disadvantages. As a result, difference-naming features quite heavily in both academic and professional writing.
The simplest kind of difference statement merely says a difference exists:
(a) Essays are different from reports.
More often, however, there is information about the nature of the difference:
(b) Unlike reports, essays usually lack subheadings.
Another cause of linguistic variety is the degree of familiarity the writer expects the reader to have with one of the contrasted ideas (not such a surprising expectation: see 156. Mentioning What the Reader Knows Already). In sentence (b), unlike shows the reader is expected to be already familiar with reports (see 56. Comparing with “Like” and “Unlike”), and that these are only being mentioned in order to make the message about essays clearer.
One way to reword (b) so as to imply reader unfamiliarity with both contrasted ideas is:
(c) Reports usually allow subheadings while essays do not.
Further linguistic variability results from the fact that differences themselves vary. Sentences (b) and (c) describe what I call an “absolute” difference: one of the compared items has something (subheadings) that the other does not. Other differences are “relative”: the compared items both have something, but in different quantities, such as focus…on the past in the following:
(d) Reports tend to focus more than essays on the past.
Even more variability of difference-naming comes from the fact that it can be done in not just one sentence as illustrated above, but also in many (or in multiple statements within one sentence), just as is the case in other key writing functions like simple example-giving, expressing consequences, restating generalizations more specifically and listing.
This post looks in depth at the numerous ways of indicating a difference in English.
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DIFFERENCE STATEMENTS IN ONE SENTENCE
1. Prepositions
The main difference-indicating preposition is unlike. It usually goes just before a familiar idea that the writer is comparing something with, and of course as a preposition it requires this idea to be in noun form or equivalent (see 84. Seven Things to Know about Prepositions, #1). The resultant preposition phrase may, like most preposition phrases, have either adjective or adverb properties.
Adjective phrases with unlike always describe a preceding noun. Sometimes there is a link verb like BE, LOOK or SEEM in between, sometimes not:
(e) Essays are unlike reports.
(f) Researchers saw structures unlike anything known.
Various other expressions can replace unlike in such sentences, although they usually seem vaguer about the expected familiarity of the idea after them. Common ones are different from/than, dissimilar to, distinguishable from, distinct from and not the same as. Different from in sentence (a) above is a straight replacement of unlike in (e).
In the above examples, there is mere mention of the existence of a difference. To say what the difference is, it is common to add in… after the unlike phrase (see 82. Common Errors in Making Comparisons, #7). The difference can be expressed with either a noun, e.g. …in length in (e), or a that statement, e.g. …in that they lack subheadings. Nouns usually name a relative difference (distance, extent, length, number, scope, size etc.), that statements an absolute one.
Adverb phrases with unlike differ grammatically from adjective ones in lacking a preceding noun to describe. They often go at or near the start of a sentence, with a following comma, a position where the familiarity suggestion is strongest:
(g) Unlike coal, nuclear fuels produce no carbon dioxide.
Sentences of this kind always say both that a difference exists and what it is.
The other common position of adverbial unlike phrases is the end of a sentence. They vary here in their need for a preceding comma, depending on meaning. Without one, they give “how” information:
(h) Traditionally, Inuit people lived unlike most other humans.
This means the traditional way in which Inuit people lived was different from that of most other humans. The nature of this difference is not indicated, but it could be with in… . Alternatives to unlike include not…like (…did not live like…) and differently from/than.
A comma before adverbial unlike…, by contrast, expresses a comparison between the verb action happening and not happening: that the verb meaning is true of the subject of the sentence (Inuit people above) but not of the noun after unlike. In (h), this would nonsensically state that Inuit people lived while most other humans did not. Sentence (g), however, could logically end with unlike coal after a comma. This would give coal the implied positive verb produce (carbon dioxide), in opposition to the negative main verb produce no…, thus saying the same as (g).
For more about unlike, (see 56. Comparing with “Like” and “Unlike”)
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2. Verbs
Verbs are often useful for paraphrasing BE + adjective (see 270. Paraphrasing Adjectives with Words of Other Kinds, #). Verbs corresponding to BE + unlike etc. include BE DISTINGUISHED FROM, DIFFER FROM and CONTRAST WITH. They can have not just one of the compared ideas as their subject, but also both, in which case they will be followed by either nothing or their preposition + each other:
(i) Essays and reports differ (from each other).
The use without a preposition is also possible with VARY. Statements naming both of the contrasted items at the start like this do not assume that the addressee has previous familiarity with either of the contrasted features. Their exact difference can be specified in either the same sentence (with in) or a new one.
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3. Conjunctions
The word while in sentence (c) above is a difference-showing conjunction. It not only indicates the existence of a difference but also requires it to be identified. Absolute differences are more likely to be involved than relative ones. When the verbs in the two contrasted statements are the same, as in (c), the second is likely to be replaced by DO (see 212. Special Uses of “Do” 1).
Alternatives to while are whereas and but. The position of whereas is similarly either before or between the contrasted ideas, but that of but is always between (see 25. Conjunction Positioning). While and whereas placed before both ideas tend to imply that the first is already familiar to the reader, like most other conjunctions in this position (see 174. Eight Things to Know about Conjunctions, #4).
The conjunction if can also contrast a unfamiliar idea with a familiar one. The difference must be a relative one between two extreme qualities. For details, see 247. Exotic Grammar Structures 6, #2.
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4. Comparatives
Comparative adjectives like shorter, adverbs like more often and pronouns like less are the main way of indicating a relative difference. This is probably because they are more informative than in phrases like different in length: a word like shorter shows not just that there is a shorter and a longer length but also which one belongs to each compared item.
To a greater extent and to a lesser extent (or not…to the same extent) are more emphatic alternatives to more and less used alone as adverbs.
Comparative ideas are not always expressed with comparative forms. Adverbs like relatively and comparatively precede a base-form adjective or adverb, e.g. relatively often, always without than… or equivalent. The preposition compared to, a possible equivalent of than, also needs to accompany base form adjectives or adverbs rather than comparative ones (see 231. Confusions of Similar Structures 3, #5). It is useful at the start of a sentence, where than is never possible, often with an adjective that would not typically describe its neighbouring noun (see 221. Multi-Word Prepositions, #3).
The combination X is one thing (but) Y is quite another says Y is a much greater problem than X (see 260. Formal Written Uses of “Thing”, #15).
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DIFFERENCE STATEMENTS IN MULTIPLE SENTENCES
As with similarities, multiple sentences can state a difference in two alternative ways. In one, the existence of the difference is stated first, then its detail:
(j) Essays are unlike reports. They…
Here, the second sentence will describe a special feature just of essays, since reports are shown by unlike to be considered already familiar to the reader. However, familiarity-assuming language is not compulsory: (j) could, for example, start Essays and reports differ, thus requiring the second sentence to say something about each, for example with whereas.
The first sentence can also be neutral about familiarity expectations, starting There is a difference (or a contrast) between… (see 161. Special Uses of “There” Sentences, #2). Often, difference will follow an adjective like major or interesting.
If the first sentence introduces a list of differences, it should include a number word or vague equivalent like various (see 122. Signpost words in Multi-Sentence Listing and 96. Avoiding Untruths 2). In There are sentences, this word will accompany the plural differences; elsewhere it can go at the end in the phrase in … ways. An alternative to ways is respects (but not aspects – see 81. Tricky Word Contrasts 2, #4).
Difference-detailing sentences like the second one in (j) should not normally have any special expression to show how they are linked to the first (see 117. Restating Generalizations More Specifically) – they just state the difference.
The other main type of multi-sentence difference-naming places one of the two contrasted ideas in the first sentence and the other in a later one:
(k) Reports usually contain subheadings. Essays, by contrast, use signpost language.
This kind of combination is very similar to the kind made with a conjunction, as in (c) above, and similarly suggests no idea familiarity. In each case, there are separate statements with separate verbs (underlined), plus an intervening difference-showing expression: while in (d) and by contrast here. The reason why a full stop is necessary here is that by contrast, though similar in meaning to while, is grammatically a different kind of word – a connector rather than a conjunction.
The need for a full stop between the relevant statements is one of various special characteristics of connectors (see 40. Conjunctions versus Connectors). Another is that connectors are not compulsory to the same extent as conjunctions: by contrast could be omitted from (k) without either changing the meaning or breaking a grammar rule.
Other connectors that act like by contrast are in contrast, however and on the other hand (but not on the contrary: see 20. Problem Connectors, #1). Also usable – again after the first sentence – are various words that express similar meaning without being a conjunction or connector. Some, such as difference, are what I have elsewhere called Synonyms of Connectors. Others are “reflexive” pronouns (see the end of 143. Subtleties of “-self” Words).
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