Making comparisons with “like” and “unlike” often suggests the similar or different point after them is familiar to the reader
WORDS THAT CAN BE USED FOR COMPARING
Comparing involves naming similarities and differences. It can be done with numerous words in English (e.g. akin, alike, as, both, comparable, likewise, reflect(s), resemble(s), similar(ly), the same, but, contrast(s), differ(s), different(ly), dissimilar, in contrast, less, more, neither, on the other hand, varies and whereas). Some of these are considered elsewhere within this blog in posts like 87. “Same As” versus “Same That”, 112. Synonyms of Connectors, 115. Describing Numerical Data and 149. Saying How Things are Similar.
The words like and unlike are used in comparisons too; but they seem to have a special additional meaning that many of the others lack, and to give a special problem to some writers as a result. In this post I wish to consider the special meaning communicated by comparisons containing like or unlike. This is not the only discussion of like. Its use for giving examples is considered in the posts 1. Simple Example Giving and 53. “As”, “Like” and “Such As”, and it also features in 98. “Very”, “Much” & “Very Much”.
GRAMMATICAL POSSIBILITIES IN COMPARING WITH “like” AND “unlike”
In written English, like and unlike are mostly prepositions, which means they combine with a following noun (without a verb) to add to the meaning of another part of their sentence. This other part can be a previous noun, in which case the un(like) phrase will be adjective-like, or anything else, when the use will be adverb-like (see 53. “As”, “Like” and “Such As” and 84. Seven Things to Know about Prepositions).
The adjective use of like and unlike phrases may be illustrated as follows:
(a) An illness (un)like influenza was produced by the new virus.
(b) The illness produced by the new virus was (un)like influenza.
Here, influenza is the noun that un(like) as a preposition needs after it, while illness is the one whose meaning the un(like) phrase is adding to in an adjective-like way. In (a), illness is placed immediately before unlike, while in (b) it is earlier and separated by the link verb was. These are the two typical positions of a noun being described by words after it (see 109. Placing an Adjective after its Noun).
The adverb use of un(like), on the other hand, looks like this:
(c) Coal stations pollute LIKE motor vehicles.
(d) Coal stations pollute, LIKE motor vehicles.
These are adverb uses because there is no noun with which (un)like can be associated: none immediately before it and none acting as the subject of a link verb like BE.
In (c), the adverbial like phrase is giving information about a verb (pollute), saying how it happens. In (d), on the other hand, where the like phrase is separated by a comma, it is the whole of the rest of the sentence that we are being informed about: the like phrase is saying that the statement made about coal stations is also true of motor vehicles. This meaning can also be conveyed by placing the like phrase at the start of the sentence, the comma after it instead of before.
The two adverb uses of un(like) phrases mirror the way some ordinary adverbs can be used in two different ways, as in the following examples from the Guinlist post 120. Six Things to Know about Adverbs:
(e) Write your name clearly in the box.
(f) Clearly, people trafficking is a serious problem.
In (e) clearly is a “manner” adverb saying how to write your name, while in (f) it is a “sentence” adverb commenting on the clarity of the entire following statement (see 121. Sentence-Spanning Adverbs).
WHEN TO COMPARE WITH “Like” AND “Unlike”
The special meaning that un(like) seems to convey in addition to that of similarity or difference is the suggestion that the idea after it is already familiar to the reader. Thus, in (a) and (b) influenza is suggested to be a familiar idea to the reader, and in (c) and (d) motor vehicles are. The suggestion of familiarity is certainly not present in many comparison words. Consider the following contrast statement:
(g) Coal stations pollute but/whereas wind farms do not.
Here, the reader is being assumed to have no previous familiarity with either of the two compared points.
Saying something that the reader knows already is perfectly acceptable if done for a suitable purpose (see 24. Good and Bad Repetition and 156. Mentioning what the Reader Knows Already). Repeating with (un)like has the suitable purpose of enabling a new point to be compared with a familiar one in order to make it clearer. Such a purpose is common but not universal in comparisons (see 149. Saying how Things are Similar).
In addition to conveying the comparison and familiarity meanings, (un)like indicates different kinds of comparison, according to whether the use is adjective-like or adverb-like. In the adjective-like use, the two compared ideas are simply the two nouns mentioned before and after – illness and influenza in (a) and (b). No indication is given of how these nouns are alike or different. In the adverb-like use, on the other hand, this additional information is provided by the accompanying verb – pollute in (c) and (d). In other words, the similarity or difference is that the meaning of this verb applies to either both of the nouns or just one.
The use of a comma to separate an adverbial (un)like phrase from the rest of the sentence, as in (d), makes a further important difference. Without one, the phrase partners the verb alone (pollute); with one, it partners the whole sentence. In the first case, the verb belongs equally to both of the compared nouns – they are both being assumed to pollute in (c) – and the similarity or difference is between the ways in which they pollute. We could paraphrase (un)like with similarly to or differently from.
In the second case, the verb belongs to the noun outside the (un)like phrase – coal stations in (d) – and the similarity or difference is whether or not it also goes with the other noun (motor vehicles): like says that it does, unlike says that its negative instead – not pollute in (d) – does. We could paraphrase like in (d) with and hence they resemble.
Here is another example, this time using unlike:
(h) Coal stations pollute, unlike wind farms.
We understand here that coal stations pollute and hence are in contrast with familiarly non-polluting wind farms. Without the comma, however, the difference would be between the pollution from the two different sources, rather than between the two sources themselves. In other words, both sources would be understood as polluters, the difference between them being the way they polluted.
A common practice among inexperienced writers of English is using (un)like at the end of a sentence, as in (h), to present a new or primary point rather than a familiar, secondary one (see 82. Common Errors in Making Comparisons). This use is sometimes found in English (in newspapers, for example), but can sound strange in professional writing. A useful alternative to unlike is shown in (g); for alternatives to like, see 149. Saying How Things are Similar.