Imagine a road in a hypothetical country  wherein it is a free-for-all situation regarding traffic rules. You can  keep to the left, if you like but none else will object if all of a  sudden, you decide to move to the right side of the road. You may take a  U-turn anywhere on the road, besides being able to cross red lights at  will. Are you already feeling slightly dizzy even imagining such a road?  A similar but far graver situation is bound to unfold if it is a  free-for-all on the road of language.  If every pedestrian and driver  moves the way he /she likes, unmindful of what others do, predictably,  it is going to create so many avoidable accidents. It is not for nothing  that grammar has been likened to the policeman of a language, whose job  is to facilitate, regulate and control the flow of thought.
We  need a certain uniformity in terms of communicating our thoughts to  others so that they are understood in exactly the same manner that we  had intended.  That is why we all need grammar  in every walk of life.  If your intention was to convey idea X and if the listener or the reader  is getting Y, you can well imagine the misunderstanding, confusion and  possibly chaos that can result consequently. Sample these hilarious but  extremely telling examples of such linguistic misinterpretation:
Written
Intended
A. Specialist in ladies and other diseases
B. Specialist in ladies' and other diseases
C. Fine for parking
C. Fine for parking
D. Fine, for parking
E. The patient had an alleviation of blood pressure
E. The patient had an alleviation of blood pressure
F. The patient had an elevation of blood pressure
You can see easily that a small mistake here or there can lead to dangerous humor and perfectly avoidable misunderstanding.
Of  course, logically speaking, any one can question the rationale behind a  particular rule, even sensing a trace of arbitrariness behind the  so-called canons of grammar. Creating a standard reference point for  grammar in any language does require developing certain do's and dont's  (which, apparently, appear to bear no inherent logic ) so as to  streamline and structure the flow of thought. But undeniably, all those  bits and pieces fit into the big jigsaw puzzle logically and  consistently, creating a beautiful and logically structured language.
Grammar  is a set of rules that one needs to follow to understand a language. To  be able to convey our meaning, we need to use proper words and create  sentences stitching them together in an acceptable and understandable  manner.
Most  competitive tests do not require you to point out the gerunds and  prepositions or other technical stuff in a sentence. If someone asks me,  “How often do you go to the cinema?” I will easily understand the  meaning of the question without even knowing that “often’ is an adverb.  Similarly, If someone asks, “Could you please pass me the book?” I know  what I have to do without knowing that ‘could’ is a modal. But most  competitive tests certainly require that you should be able to use all  these finer grammatical points while writing good English.
What  most often comes to mind when someone utters the word grammar, is the  vocabulary of grammar : modals, prepositions, conjunctions, adverbs etc.  Inability to describe words in grammatical terms is not a crime but it  is definitely a big drawback if you cannot even put the words and  phrases in their proper place.
Always  remember, a grammatically wrong sentence most often does not convey the  right meaning., unless it is a very private kind of code. So it is for  our benefit that we learn certain basic grammar rules to understand the  language. And when we know the language well, we can use idioms,  phrases,  give examples, convince people,  emphasize certain points,  argue and so on. As someone has rightly said, “You do not need perfect  grammar to communicate. You do need it to communicate well. Excellent  grammar allows people to find nuances in the language that escape those  who cannot construct a technically complex sentence correctly.”
Let us have a look at some common errors in conversation due to lack of grammar knowledge:
Wrong: He is very miser.
Right: He is very miserly.
Wrong: This book is more better.
Right: This book is better.
Wrong: To make dolls is his profession.
Right: Making dolls is his profession.
Wrong: One must do his duty.
Right: One must do one’s duty.
Wrong: He gave a speech.
Right: He made a speech.
Wrong: I do not like the poetries by Wordsworth.
Right: I do not like the poetry by Wordsworth.
Wrong: He invited me on tea.
Right: He invited me to/for tea.
Seeing these common blunders, you must have got a fairly good idea about the need for studying grammar.
Hence,  the study of grammar enables us to go beyond our instinctive,  native-speaker knowledge, and to use the language in an intelligent,  informed way. In more general terms, a knowledge of grammar is part of  our knowledge of the world and of ourselves.
Getting Back To Basics
To  be able to spot error in a given sentence, it is essential to know how a  sentence is actually written. To begin with, a sentence is a meaningful  group of words arranged in a logical order. Taken together, the entire  sequence of words in a given sentence must make complete sense. In case a  group of words carries incomplete sense, such a sequence would be  better called a phrase e.g.
In a corner, in the lurch, in the sky etc.
A  typical sentence would contain a subject and a predicate. Very simply,  the subject in a sentence is the focus of discussion i.e. the person,  object, event or idea about which something has been said. The rest of  the sentence is labeled as the predicate. Have a look at the following  cases (The words given in bold italics are subjects):
Man is mortal.
Rosa was beautiful.
I cannot tolerate this kind of indiscipline.
One of the safest ways to decide the subject would be to ask a question the answer to which will be your subject in that case.
Man is mortal. (Who is mortal?, Man)
Rosa was beautiful. (Who was beautiful?, Rosa)
I cannot tolerate this kind of indiscipline. (Who cannot tolerate this kind of indiscipline?, I)
It  is extremely important to ask the right kind of question to be able to  decide he subject correctly. A wrongly framed question is bound to  elicit a wrong answer. Let us have a look at some more complex cases:
  Truly sweet are the fruits of labor. (What are truly sweet? fruits )
Tweety slept on the floor.(Who slept on the floor? Tweety)
Up went the kite. (What went up? Kite)
The first and the last one could also have been written as
The fruits of labor are truly sweet. (Fruits is the subject here)
Tweety slept on the floor.(Tweety is the subject)
The kite went up.(Kite is the subject)
A sentence can have a maximum of eight parts of speech. Of course, you can have a sentence with fewer, say three, four or five parts even.
1. Noun: The name of a person, place or thing. Since mostly we discuss these three things, a great majority of all the existing words are nouns only.
2. Pronoun: A word used in place of a noun e.g. he, she, it, you, they, who,
3. Adjective: A word used to tell us about the quality of a noun or pronoun e.g. tall, good, beautiful etc
4. Verb: Is used to describe an action e.g. walk, eat, play, read etc. Is, Am. Are, Was, Were are helping verbs because they describes states of existence and not any action happening.
5. Adverb: Is used to qualify a verb, adjective or another adverb
6. Preposition: Is used used with a noun/ pronoun to describe how the person/ thing denoted by it stands vis a vis others
A. She was sitting in the chair
B. She was siting on the chair
C. She was sitting at the gate.
(Do you notice the difference in meaning?)
7. Conjunction: Is a word used to join together two sentences or two parts of the same sentence e.g.
A. They tried hard but did not succeed
B. He and I will work together.
8. Interjection: Used to express a strong feeling e.g.
A. Aha ! We have won the match
B. Bravo ! You have made us proud
C. Alas ! We have been done in by the crook.
Better
A. He bettered his own record.(better is used as a verb here)
B. This is a much better option. (better is used as an adjective here)
C. He knows he her better than I do. (better is used as an adverb here)
D. Give preference to your betters. (better is used as a noun here)
1. EVEN
A. Every alternate number happens to be even.(adjective)
B. The leader tried to even out the rough edges.(verb)
C. Do you even think of such a possibility in future?(adverb)
2. RIGHT
A. Two wrongs do not make a right.(noun)
B. To right this wrong, we require a lot of efforts.(verb)
C. None of your rights has been violated.(noun)
D. The right course of action is to ignore him.(adjective)
E. She played right in the end. (adverb)
3. FAST
A. I do not fast at all.(verb)
B. These are fast colors and do not fade quickly.(adjective)
C. Please run fast else you will miss the show.(adverb)
D. The fast he undertook lasted fourteen days.(noun)
4. ALL
A. I have been looted of all I had.(noun)
B. All humans are mortal.(adjective)
C. At the meeting, all spoke of the dishonor he had brought them.(pronoun)
5. IN
A. Please come in.(preposition)
B. This kind of dressing style is the in thing.(adjective)
C. We were done in by the her laziness. (adverb)
The fruits of labor are truly sweet. (Fruits is the subject here)
Tweety slept on the floor.(Tweety is the subject)
The kite went up.(Kite is the subject)
So  the subject remains the same in all the three cases even upon  rephrasing the entire sentence. This fact leads us to an important  conclusion - The subject is not a matter of location; it  is actually a  question of logic. A subject can be present anywhere  in the sentence :  the beginning, the end or the middle.
Once  you are able to decipher the subject, more than half the battle is won.  The next step would be to make sure it agrees well with the verb /  helping verb in the sentence. This is one of the most basic and  important starting points for the process of finding an error in a  sentence. The rest i.e. checking for the right tense, adjectives,  adverbs, prepositions, conjunctions etc. should follow it. You will  learn more about these things in the following chapters in this module.  Nevertheless, here is a listing of the eight major parts of speech which  should be of interest and relevance to you.
A sentence can have a maximum of eight parts of speech. Of course, you can have a sentence with fewer, say three, four or five parts even.
1. Noun: The name of a person, place or thing. Since mostly we discuss these three things, a great majority of all the existing words are nouns only.
2. Pronoun: A word used in place of a noun e.g. he, she, it, you, they, who,
3. Adjective: A word used to tell us about the quality of a noun or pronoun e.g. tall, good, beautiful etc
4. Verb: Is used to describe an action e.g. walk, eat, play, read etc. Is, Am. Are, Was, Were are helping verbs because they describes states of existence and not any action happening.
5. Adverb: Is used to qualify a verb, adjective or another adverb
A. She did the job efficiently.(efficiently qualifies did, a verb. Therefore, efficiently plays the role of an adverb here)
B.  The evening was quite romantic.(Romantic tells us about the evening, a  noun. Thus romantic is an adjective  as per our definition. The word  quite further tells us about romantic. Hence quite is an adverb here)
C.  They played to the gallery, very much expectedly.(expectedly is an  adverb because it qualifies play, a verb here. Very much further  qualifies it. Therefore, very much happens to be an adverb here. )
6. Preposition: Is used used with a noun/ pronoun to describe how the person/ thing denoted by it stands vis a vis others
A. She was sitting in the chair
B. She was siting on the chair
C. She was sitting at the gate.
(Do you notice the difference in meaning?)
7. Conjunction: Is a word used to join together two sentences or two parts of the same sentence e.g.
A. They tried hard but did not succeed
B. He and I will work together.
8. Interjection: Used to express a strong feeling e.g.
A. Aha ! We have won the match
B. Bravo ! You have made us proud
C. Alas ! We have been done in by the crook.
Please  note carefully that a word is a versatile actor, not a stereotyped  performer. It could assume infinite number of roles, depending on the  way it has been used in a given sentence. Have a look at the following  example:
Better
A. He bettered his own record.(better is used as a verb here)
B. This is a much better option. (better is used as an adjective here)
C. He knows he her better than I do. (better is used as an adverb here)
D. Give preference to your betters. (better is used as a noun here)
The  best way to decode the role played by a word in a given sentence is to  take out its intended contextual meaning and replace the word with its  meaning. The resulting role of the intended meaning is the role played  by the word. For instance, in sentence D above, betters actually means  better people. Since people is a noun, better must be a noun here. You  can practice with the following  sample questions:
1. EVEN
A. Every alternate number happens to be even.(adjective)
B. The leader tried to even out the rough edges.(verb)
C. Do you even think of such a possibility in future?(adverb)
2. RIGHT
A. Two wrongs do not make a right.(noun)
B. To right this wrong, we require a lot of efforts.(verb)
C. None of your rights has been violated.(noun)
D. The right course of action is to ignore him.(adjective)
E. She played right in the end. (adverb)
3. FAST
A. I do not fast at all.(verb)
B. These are fast colors and do not fade quickly.(adjective)
C. Please run fast else you will miss the show.(adverb)
D. The fast he undertook lasted fourteen days.(noun)
4. ALL
A. I have been looted of all I had.(noun)
B. All humans are mortal.(adjective)
C. At the meeting, all spoke of the dishonor he had brought them.(pronoun)
5. IN
A. Please come in.(preposition)
B. This kind of dressing style is the in thing.(adjective)
C. We were done in by the her laziness. (adverb)