Effective Communication


Before knowing how to express certainty, probability or possibility, it is important to know the basics first.

There is a verb called “modal”. It is a type of auxiliary verb used to express modalities. It is the state or “modes” in which a thing exists in general, such as possibility, ability, prohibition, and necessity.

In this article, you will be taught how to express certainty, probability and possibility for effective communication.


According to the Merriam-Webster Dictionary, certainty means being free from doubt or being confident about something. There are modal verbs that express certainty. It can be used to express the present by using “must”, “can’t”, and “couldn’t”

Sentence examples:

  1. You must go to the barangay health care today for COVID-19 vaccination.
  2. I can’t go to school today because my head is aching.
  3. I couldn’t find my laptop this afternoon.
  4. Jenny must pass her assignments this evening.
  5. I couldn’t trade my money for those fruits.

Meanwhile, it can be used to express certainty in the past by using “must have”, “can’t have” and “couldn’t have”. It must be used to mean that something was not possible in the past. Like, it would have been different. Thus, the formula for creating a sentence using this is: subject + can’t have / couldn’t have + past participle

  1. I must have eaten before I went to school this morning.
  2. He can’t have driven in Beverly Hills.
  3. Jeff couldn’t have told me this morning because I was not there and I left my phone at my house.
  4. I must have gotten the necklace earlier.
  5. I couldn’t have all the things I want in life.


According to the Merriam-Webster Dictionary, probability means being probable or likelihood of something (event or circumstance). Like certainty, there are modal verbs that can be used to express either probability in the present or future by using “should” and “ought to”.

Sentence examples:

  1. My brother should go to the doctor for treatment and medications.
  2. I ought to buy a banana every day as a potassium source for my feet.
  3. I ought to leave by now.
  4. I should go directly to my husband’s office.
  5. One hour ought to be enough time.

Also, it can be used when we talk about the past by using “should have” and “ought to have”. The formula for creating a sentence using it is: subject + should have / ought to have + past participle

  1. I should have called Jenny sooner.
  2. My clothes got wet yesterday when I went to school. I should have taken an umbrella with me.
  3. They ought to have a waiting shed near the school.
  4. I often think that I ought to have bought oranges, not apples.
  5. Gary should have brought the printer.


From the word “possible”, it means something that is able to be done. It can be expressed by using  “could”, “may” and “might to” to talk about the possibility of something either in the present or in the future.

Sentence examples:

  1. I could buy you fruit when I go to the supermarket this afternoon.
  2. I may go now.
  3. I might see you this Wednesday or Thursday.
  4. I might go to the dentist tomorrow for the adjustment of my braces.

Remember, when you write a formal paper for school or work, you should not shortcut “should not” or “could not”. In short, avoid using apostrophes in scientific and medical writing because it is considered informal.

By the next time you communicate to someone and you are in the state of certainty, being probable, or something that can be done either in the past, present, or future, you already know what to use and how to use the modal verbs.

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Gabrielle Love Acero

Gabrielle Love Acero loves to write in any form since she was still a little girl. Her writing skills were enhanced through reading books, articles, and informative materials such as Reader’s Digest. They are also her hobbies. She began her blog site at the age of 11. She wrote her experiences in life. With her experiences, she became a scriptwriter during her High School years. One of her movies that she directed and produced won 2nd place against 7 high school institutions (public and private) in the city where she is living. The interschool competition was hosted by Commission on Population (PopCom) – Region X. She puts effort into doing these things because it is her passion. She is one of the top of the class during her Elementary and High School years. She graduated as the Class Valedictorian in Junior High School. At the age of 9, Gabrielle Love Acero started participating and engaging in voluntary activities, especially at church. She entered the kids’ choir and joined “Sidewalk Saturday School (SSS)” as a volunteer. She taught indigenous children about God and His love for them in a certain area, including skit-playing and Bible-reading. With those experiences, she continued being a volunteer at heart until the present day. At the age of 13, she became a Worship leader in the church where she is currently attending since 2007. Her dedication, commitment, and love for God and His people made her become one of the assets of the church. She is one of the youth leaders. Gabrielle Love Acero is currently a junior student of Bachelor of Science (B.S.) in Medical Biology at Xavier University – Ateneo de Cagayan, where she continues to work towards her dream of becoming a doctor in the near future. She is also involved in extracurricular organizations. She is currently the President of Xavier University Red Cross Youth (XU – RCY), where she plans, organizes, and implements humanitarian activities for the community with her team. Also, she is a 1st class Cadet Officer at Xavier University Philippine Air Force - Reserve Officer Training Corps (XU PAF ROTC), where she teaches basic military trainings based on her military training experiences. Also, she implies military leadership to her lower classes. Not despising her Biology degree, she put her efforts into her studies and get involved in Biophilic (Biology) Society activities with her colleagues. Many people are awed by her experiences and involvements, especially her time management skills, but with humility, she believes that her life is not her own, but with a purpose. Gabrielle Love Acero hopes to learn more about life and the field she is currently in. She is goal-oriented and exemplifies excellence in everything she does, not because of herself, but because of the greater One living inside her.