Full stops depend on grammar, not meaning. A full stop is needed before every new verb, unless there is a “joining device”
THE RELATION BETWEEN GRAMMAR AND PUNCTUATION
Punctuation is often presented as a matter of feeling or style, when in reality it is mostly (but not completely) determined by grammar. This point is made in various other punctuation posts within these pages, particularly 17. Colons versus Semi-colons, 34. Relative Pronouns and Commas, 50. Right and Wrong Comma Places and 58. Optional Apostrophe Endings.
Full stop usage is almost wholly determined by grammar. Any explanations that do not involve it are likely to prove vague and confusing. In this post I wish to show why that is so, and to describe the grammar in a way that my own students seem to have found useful. Much of what I have to say is also in my book Grammar Practice for Professional Writing.
COMMON BUT UNHELPFUL WAYS TO UNDERSTAND FULL STOPS
A natural first step in investigating full stop use is to consider what a sentence is. One unhelpful definition is “a group of words beginning with a capital letter and ending with a full stop”. The problem with this, of course, is that, while it may assist readers to recognise a sentence in a text, it is of little value to writers needing to know when a full stop should be written in the first place.
Another common but problematic definition calls sentences “complete thoughts” or “complete statements”. The problem is the meaning of “complete”. One difficulty with it is that the “complete thought” of any particular sentence can usually also be expressed in less or more than a sentence. For example, the “thought” of the sentence Plants use the energy of sunlight is surely unchanged in both the part-sentence phrase plants using the energy of sunlight and the two-sentence Plants use energy. It comes from sunlight (for more on the possibilities of paraphrase, see 80. How to Paraphrase).
The second difficulty with the idea of “complete” is that defining it to exclude paraphrases like the above is only possible with concepts from grammar – and if grammar has to be brought in to define a sentence, then why use the term “complete” at all? Some writers try to get around this by saying that sub-sentence statements “do not make sense”, but the fact is that they do – it is their grammar that is at issue, not their meaning (see 100. What is a Grammar Error?).
THE NEED TO RECOGNIZE VERBS AND JOINING DEVICES
A much clearer definition of a sentence can be achieved by means of the grammatical concept of verbs: a sentence is not complete until it has a verb, and if another verb has to be used, there must be a new sentence, unless there is some special language to “join” the two verbs together. The centrality of verbs in sentences rather resembles the centrality of vowels in syllables (see 125. Stress & Emphasis). Therefore, the main requirement for correct full stop use is ability to recognize first verbs and then the language that can join them together (“joining devices”).
Verbs can be recognized in different ways. Some people make use of the special meanings or forms that can be added to most verbs: “tenses” (past, present, future, etc), “voices” (active or passive), and “moods” (indicative, imperative, subjunctive). Others have some success with the endings found on many verbs: -s, -ing, -ed, -en, -ify, -ate, etc. (but for a potential problem with this, see 172. Multi-Use Suffixes). Others again make do with the traditional notion of verbs being words of “doing” or “being” (even though “actions” can be expressed by other kinds of word besides verbs – see 31. Prepositions after Action Nouns 1).
Personally, I find it useful to recognise that a verb is almost any word that sounds possible after will. This test easily identifies GO, HAVE, BE, WALK, EVAPORATE and RECOMMEND as verbs, and it rules out words like FROM, HAPPY, TOMORROW and RECOMMENDATION (the main problem is with word variations like went, having, was, had and evaporated, which have to be changed to their base forms before the will test is used).
JOINING DEVICES IN ENGLISH
The name “joining device” is my own. It would be convenient to say “joining word” instead, but unfortunately some of the possibilities are less than, or more than, a word, and “device” is the only general term I know that gets round this problem. Below is a classification of joining devices. It contains categories that can sometimes be clicked on for more information, and example sentences with the joined verbs written in CAPITALS.
There are two subtypes of conjunctions: “subordinating” and “coordinating” (see 174. Eight Things to Know about Conjunctions). Subordinating ones include IF, AFTER, ALTHOUGH, AS, BECAUSE, SINCE, BEFORE, THAT, UNTIL, WHEREAS and WHILE. Here are two verbs linked together by AFTER:
(a) After the sun SETS, mosquitoes BECOME active.
Coordinating conjunctions are not so numerous. The main ones are AND, BUT, OR, SO and YET. Sometimes they form pairs like BOTH…AND, EITHER…OR and JUST AS…SO (see 64. Double Conjunctions), e.g.:
(b) Cycling both PROMOTES health and PROTECTS the environment.
2. Relative Pronouns and Relative Adverbs
(c) People who LIVE in glass houses SHOULD NOT THROW stones.
(d) 1914 WAS the year when the first world war BEGAN.
3. Question Words in Indirect Questions
(e) Plato WONDERED where perfect forms EXIST.
4. Special Additions to Verbs
(f) PUNCTUATing sentences correctly NEEDS concentration.
5. Colons and Semi-Colons
(g) Demand AFFECTS prices; heating oil IS dearer in winter.
This is a fairly complete list of joining devices. An important final point to note is that some words exist in English that seem to be joining devices but are not. The most important of these are connectors like therefore, however, in fact, then and furthermore. For a full analysis of how connectors differ from conjunctions, see 40. Conjunctions versus Connectors. For examples of connectors misused as joining devices, see 138. Test Your Command of Grammar.
PRACTICE IN RECOGNIZING JOINING DEVICES
A possible procedure for recognizing where to put a full stop is to check whether a new verb has a joining device with it; if there is no joining device, a new verb needs a full stop somewhere before it. In general, sentences always need one fewer joining device than they have verbs. Thus, a sentence with one verb must have no joining device, a sentence with two verbs needs one joining device, and a sentence with 100 verbs needs 99 joining devices. Here are two exercises that offer practice in spotting verbs and joining devices.
EXERCISE 1: Decide whether a comma or a full stop is needed in each space below. If you think a comma is right, identify the joining device linking the underlined verbs. Answers are below.
1. 21 is not a prime number ___ It/it can be divided by 7 and 3.
2. Tropical forests need to be protected ___ Which/which is not always easy.
3. Since cigarettes are very addictive ___ Cigarette/cigarette taxes hardly put off smokers.
4. However hard you try ___ You/you cannot make a machine work without fuel.
5. First log out from your account ___ Then/then switch off the computer.
6. Every country has a police force ___ Because/because human societies cannot function without order.
7. The ancient Romans were clever engineers ___ This/this meant (that) they/they built good roads.
8. Eating fruit brings numerous health benefits ___ So/so doctors recommend it more and more.
ANSWERS: 1 = full stop; 2 = comma (which); 3 = comma (since); 4 = comma (however – note that this is a relative adverb here, not the normal connector); 5 = full stop; 6 = comma (because); 7 = full stop (this sentence has three verbs but only one joining device: that joining meant and built); 8 = comma or full stop (some writers allow so to be an informal connector as well as a conjunction)..
EXERCISE 2: Write either a comma or a full stop in each space marked … below. Change any letter following a full stop into a CAPITAL.
Priests are generally full-time male specialists who officiate at public events … they act as a link between ordinary people and their god or gods … they have very high status … some priests even being distinguished from other people by special clothing or hairstyles … in most societies, priests obtain their position through inheritance or political appointment … the training of priests can be hard and long … it involves learning the beliefs and ritual of their religion … while time must also be spent on fasting, praying and doing manual work … though the priest rarely receives a fee for his services … he is supported by donations from the people he serves … the priestly office can involve a high political position … for example in some countries even a head of state can be a priest.
ANSWERS: (where a comma is necessary, the relevant joining device is underlined).
Priests are generally full-time male specialists who officiate at public events. They act as a link between ordinary people and their god or gods. They have very high status, some priests even being distinguished from other people by special clothing or hairstyles. In most societies, priests obtain their position through inheritance or political appointment. The training of priests can be hard and long. It involves learning the beliefs and ritual of their religion, while time must also be spent on fasting, praying and doing manual work. Though the priest rarely receives a fee for his services, he is supported by donations from the people he serves. The priestly office can involve a high political position. For example, in some countries even a head of state can be a priest.