This is a simple explanation of the two terms as I understand them:
Coherence is combined by many different factors that make the each paragraph and each sentence to contribute to the meaning of the whole text. The sentences are like photos that you take during your summer vacation. You put them together and you have the whole story of your “summer vacation in photos”. Each of the photos participates in the meaning of the whole text. You can’t put among them the photos of your parents’ winter vacation, because these photos do not fit your topic “my summer vacation”. So, the information given in each of your sentences should be relevant to the topic of the whole text.
Whereas cohesion is a link that you use in order to connect one sentence to another using some techniques: repetition of the word from the first sentence in the second one, use of synonyms, antonyms, pronouns, collocations, enumerations, parallel structures, conjunctions etc. Take the photos of your summer vacations and put them together like sentences in your text. Now tell the story. The order in which photos are presented and the way you put the sentences together is the cohesion of the text. The information of the next sentence includes some familiar information mentioned in the previous one. The idea is easy to follow because of the use of the links that make the text logical. If you add some information, you can use “and”; if you contradict previously mentioned idea you can use “but”; if you talked about a boy in the previous sentence, you can not start next sentence with the pronoun “she”, but you can use “he” in it.
You can find more on the internet. You can read this pdf file that contains a lot of examples and clearly distinguish these two terms:
http://cs.illinois.edu/class/fa09/cs498 ... re25HO.pdf Hope it could be helpful. Good luck with your tefl on line course!
