To understand the subject-verb agreement, one should first know what is the subject of a sentence. The topic of the sentence is referred to as the subject. It is the main idea that the sentence seeks to explain and elaborate upon. Verbs, on the other hand, refer to verbs that denote any kind of action. 

The verb of the sentence has to be adjusted and altered in a form that agrees with the subject. One noteworthy point is that the number(singular or plural) and pronoun play a major role in the kind of verb required in those cases.

The subject-verb agreement is determined by a set of rules. A proper and in-depth understanding of these rules is an important part of studies in English Grammar. Although most of these rules are quite straightforward, some of the aspects are slightly complicated and require a deeper analysis for an effective understanding of the topic.

Rules

Subject-verb agreements are based on certain rules that need to be followed in order to maintain correctness. 

• The verb must agree with the subject, in terms of number, that is, if the subject is singular, the verb used must be also singular. For example:

1. My friend has come to meet me (singular subject-“My friend”, singular verb- “has”).
2. They have arrived (plural subject-“They”, plural verb-“have”)

• When the subject consists of nouns or pronouns joined by a conjunction such as “and” or “or”, a plural verb is used. For example:

1. I and my teammates practice every day.
2. Jackie and Grace like each other.

• When there is just one subject and more than one verb, the entire group of verbs must agree to the same subject, that is, each verb should follow the agreement rules individually. For example:

1. Sports are a great excuse for exercising and make up for the monotonous and unhealthy lifestyle followed by today’s generation (plural subject “sports” with plural verbs throughout the sentence).
2. Ryan is an ideal student and is a likeable fellow (singular subject “Ryan” with singular verbs throughout the sentence).

• Some words like either, neither, each, everyone, anyone, anybody etc. use a singular verb for agreement. For example:

1. Neither of the suspects was speaking the truth.
2. Either he or she had to take action.
3. Everyone was happy and satisfied that day.
4. Each student is supposed to take care of self belongings.

• In cases where there are multiple subjects in the sentence, the verb must agree with the one closest to it. For example:

1. The teacher or the students have done the decorations.
2. The students or the teacher has done the decorations.

• In cases where two or more subjects are joined by phrases like ‘as well as’, ‘along with’ or ‘with’, the verb must agree with the first subject. For example:

1. The principal as well as the teachers were present that day (singular verb with the singular first subject).
2. Lions with a leader are a ferocious creation (plural verb with the plural first subject).

• Uncountable nouns are always followed by singular verbs. For instance:

1. Education is the gate to success.
2. Health is the greatest asset.

• Nouns such as scissors, tongs, trousers or any article which is used in pairs, take a plural verb. For example:

1. These scissors are very sharp.
2. The trousers have completely worn out.

• Nouns which are plural in appearance or form, but are effectively singular in use, take a singular noun. For example:

1. The news is very interesting.
2. Calculus is an important mathematical concept.

• Some countable nouns which are plural in form also take a plural verb. For example:

1. The wages for labourers have been quite low this year.
2. The earnings have been adequate.

• Nouns that are singular in form, but plural in meaning take a plural verb. For example:

1. Fish are aquatic animals.
2. Police have initiated a nationwide man-hunt to look for the fugitives.

• Collective nouns are considered a singular subject in the agreement rules and take a singular verb, even though they represent a group. For example:

1. A pride of lions was walking down the road.
2. A flock of sheep was grazing in the fields nearby.

1. Sentences that begin with the phrase “there is” or “there are”, have their subjects followed by the verb and the verb agrees to whatever subject that follows it in the sentence. For example:

1. There is a town nearby.
2. There are rumours of a war waging in the north.

Exceptions

There are a few exceptions to the subject-verb agreement’s set of rules. There are a couple of exceptions that are of primary importance.

1. There are a clear set of definite pronouns which take a singular or a plural value. However, there is a third category of these pronouns which can either take a singular or a plural value. For example:
   some, any, none, all, most etc.
   
   
2. Usually, when collective nouns are the sole subject, singular verbs are used. However, when the collective nouns denote a plurality of individuality(where the collective noun is not the only subject), plural nouns may be used. For example: 

The travel group have asked for their dinner(“their” denotes individuality).

Exercises

A few unsolved exercises have been listed below for practice purposes:

1. Teacher and student  ____ complementary to each other (is/are).
2. The students as well as their teacher ____ enjoying a picnic in the garden (is/are).
3. A flock of sheep ____ seen nearby (was/were).
4. Children ____ completed their assignments (has/have).
5. Football and cricket ____ the most popular games (is/are).
6. Ronny ____ not ____ what to do (do/does; know/knows).
7. The fugitive with his whole gang _____ disappeared (has/have).
8. Everyone aboard the train ____ scared (was/were).
9. Either one of them ____ the knowledge of the whole event (has/have).
10. Neither of them ____ known to be vigilant (is/are).

Conclusion

The subject-verb agreement lays out the suitable agreements and rules between subjects and verbs which need to be followed while structuring a sentence. These rules give the possible structure of the sentence by pre-determining the subjects with possible verbs. One should be thorough with them t avoid any mistake while speaking or writing.