If you think these two terms are interchangeable, I am sorry to be the one to tell you that despite being related, coherence and cohesion mean different things.
Let us first talk about coherence. Simply put, it is what makes a text intelligible. That means that the ideas confined within the text must logically connect and work with each other in order to form an understandable whole. Thus, from now on, you will adhere to the following definition:
COHERENT (adj.)
logically ordered and connected;
clear and consistent;
comprehensible.
There are, however, some things to beware of so as to make sure your text will not become incoherent. Firstly, if a detail in a text is not related to the topic of the paragraph in which it is presented, the text will not be coherent (I will make a guide on those terms soon). Secondly, to establish coherence, you must make sure to make your text concise, as well as cohesive. Read the text below:
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I love playing videogames, but ants can carry more than ten times their body weight. Moreover, I do not like tea, so my dog ate my homework and I forgot to take my daughter to school.
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Clauses and sentences are connected in that text, but are ideas? No. Therefore, that text is cohesive, but not coherent.
Which leads me to the next term: cohesion. Read attentively:
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Cohesion refers to the way in which words, phrases, sentences and paragraphs link together to create a text that flows logically in structure and meaning from beginning to end.
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Have you already spotted the difference?
If you have not, I will give you a hint: both coherence and cohesion mean connection, but each connects different things.
Whereas coherence links ideas, cohesion links the elements of the text (e.g. clauses). Cohesion can be achieved by the use of cohesive devices and you must know multiple in order to write better texts. Fear not, for I will show you the most important ones. Take a look!
First, you must learn how to use conjunctions like these and believe me when I tell you that they go a long way.
After you have learnt how to properly utilize fancier conjunctions, you can move on to a more complete list like this one. So as to facilitate your leaning process, I will leave some sentences you can use as examples whenever you have to use those words.
Of course, those are not all of them. There are still many more, but most of them can be either too academic or too rarely used to be in the list, such as "albeit", "henceforth", "heretofore", "lest", and "thereupon".
How about doing some exercises?
Below, you will find an exercise extracted and adapted from Objective Proficiency, a book published by Cambridge English.
First, read the texts below:
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Text 1:
Recently, a politician was mocked in the press for having a digitally enhanced poster of himself produced. Gone were the receding hairline and wrinkles and a younger, more attractive face peered down from the hoarding. However, there does seem to be evidence that, although they may be unaware of it, a considerable number of people vote according to a candidate’s looks. A scientific experiment which used photos of just under 2,000 political candidates and over 10,000 voters took place recently. It found that if a candidate was attractive, then both men and women were more likely to believe that he or she was trustworthy and very able. When a candidate’s educational background and occupation were included as an additional check, it was found to have no effect.
Text 2:
The images we see on magazine covers today are not what they used to be. A few clicks of the mouse on Photoshop can easily transform models and celebrities into living Barbies. It seems as if advertisers and photojournalists are on the quest to define and sell ‘ideal beauty’. Female models have their spots and wrinkles airbrushed out, their legs and eyelashes are made to look longer than they really are and faces magically become more symmetrical. Perhaps the time has come for legislation prohibiting editors from using these techniques? Or, maybe, as some people think, all this is nothing new. Artists have been doing something similar for centuries and we have accepted it as normal.
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Now look at this summary of the two texts. There are five linking words missing. Decide which answer A, B or C, best fits each space.
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According to the first text, research has shown that both people involved in the political process and, (1), the public at large, unconsciously give more weight to a candidate’s attractiveness than to their background skills. (2), good-looking candidates were seen to possess very positive personal qualities.
Text B puts forward the opinion that (3), modern technology enables people in the media to idealize faces and bodies. It (4) goes on to question whether this is really a problem and (5) it asks whether this issue is entirely modern.
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1- a) thus b) additionally c) finally
2- a) Moreover b) Then c) On the other hand
3- a) although b) besides c) firstly
4- a) besides b) then c) therefore
5- a) finally b) equally c) although
Do not worry if you fail to do this exercise. It is C2 level, after all. I will explain why the following answers are correct:
1- b
2- a
3- c
4- b
5- a
The first answer is "additionally" because the research analyzed both "people involved in the political process" and "the public at large". If you only quickly read the text, you could think of answering "thus" as this word is often used in sentences with that structure. However, if you stop to think about it, "the public at large" embodies the entire population and "people involved in the political process" is a part of that whole which integrates only people who are politically active. Therefore, a relationship of result would be inappropriate.
The second answer is "Moreover" because what the writer wishes to convey is that besides people placing more importance on a "candidate's attractiveness" rather than on their skills, those who are attractive are judged by the population to have more qualities.
The third one is "firstly" because the writer wishes to establish order in the paragraph to more easily add more information afterwards.
The fourth one is "then" and is very straight forward because the author uses "firstly" in the beginning, which makes it predictable that the order of elements mentioned is to be maintained.
The fifth one is "finally" because again, the author establishes an order so as to make the text more organized and easier to read.
Now, read the following text and try to identify as many cohesive devices as you can.
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Undoubtedly, education in Brazil needs many improvements. For instance, most people agree the Brazilian government should invest more in public schools as it is obligated to offer formal education to all children and teenagers.
Public schools in Brazil have, for the most part, precarious infrastructure and are overcrowded. Another problem is that many teachers are not qualified enough for teaching.
I tend to think that, in the future, schools will hire more competent and experienced teachers and increase their salaries. Therefore, the quality of education will be superior. I also think that technology will be more used for obtaining knowledge. In summary, education in Brazil is not very good, but it could get a lot better with some effort.
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Before I show you the answers, I just wanted to point out that this is a perfect example of a text that is both coherent and cohesive. Not only do the ideas in it connect, but also words, phrases, clauses, sentences, and paragraphs. Now, check how many you found.
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Undoubtedly, education in Brazil needs many improvements. For instance, most people agree the Brazilian government should invest more in public schools as it is obligated to offer formal education to all children and teenagers.
Public schools in Brazil have, for the most part, precarious infrastructure and are overcrowded. Another problem is that many teachers are not qualified enough for teaching.
I tend to think that, in the future, schools will hire more competent and experienced teachers and increase their salaries. Therefore, the quality of education will be superior. I also think that technology will be more used for obtaining knowledge. In summary, education in Brazil is not very good, but it could get a lot better with some effort.
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Notice that some words like "and" and "but" are highlighted here but are not in the complete list I showed you. That is because they are common lexis, which basically means that they are used everywhere. Ordinarily, I would not have highlighted them, but since this is a guide, I thought I should.
Also, even though the expression "I tend to think" is not in the list, it enhances cohesiveness regardless and is thus highlighted as well.
Now you are on your own. I will leave a link to an activity concerning cohesion below. Only as a means of comparison, I would say it is suitable for C1 and C2 learners of English. Use the information of this guide to help you.
To sum up, coherence is the connection between the ideas of the text, whilst cohesion is the connection between the elements of it.