Table of Contents, Thinking Tools Resources Page Previous Section, Thinking Tools Next Section, Thinking Tools

Distinguishing Between Inferences and Assumptions

As we have said, the elements of reasoning interrelate. They are continually influencing and being influenced by one another. We now will focus at length on the crucial relationship between two of the elements: inference and assumption. Learning to distinguish inferences from assumptions is an important skill in critical thinking. Many confuse the two elements. Let us begin with a review of the basic meanings:

  1. Inference: An inference is a step of the mind, an intellectual act by which one concludes that something is true in light of something else's being true, or seeming to be true. If you come at me with a knife in your hand, I probably would infer that you mean to do me harm. Inferences can be accurate or inaccurate, logical or illogical, justified or unjustified.

  2. Assumption: An assumption is something we take for granted or presuppose. Usually it is something we previously learned and do not question. It is part of our system of beliefs. We assume our beliefs to be true and use them to interpret the world about us. If you believe that it is dangerous to walk late at night in big cities and you are staying in Chicago, you will infer that it is dangerous to go for a walk late at night. You take for granted your belief that it is dangerous to walk late at night in big cities. If your belief is a sound one, your assumption is sound. If your belief is not sound, your assumption is not sound. Beliefs, and hence assumptions, can be unjustified or justified, depending upon whether we do or do not have good reasons for them. Consider this example: "I heard a scratch at the door. I got up to let the cat in." My inference was based on the assumption (my prior belief) that only the cat makes that noise, and that she makes it only when she wants to be let in.

We humans naturally and regularly use our beliefs as assumptions and make inferences based on those assumptions. We must do so to make sense of where we are, what we are about, and what is happening. Assumptions and inferences permeate our lives precisely because we cannot act without them. We make judgments, form interpretations, and come to conclusions based on the beliefs we have formed (see Figure 6.5).

Figure 6.5. Humans routinely draw conclusions in situations. Those conclusions are based on assumptions that usually operate at an unconscious level.


If you put humans in any situation, they start to give it some meaning or other. People automatically make inferences to gain a basis for understanding and action. So quickly and automatically do we make inferences that we do not, without training, notice them as such. We see dark clouds and infer rain. We hear the door slam and infer that someone has arrived. We see a frowning face and infer that the person is angry. If our friend is late, we infer that she is being inconsiderate. We meet a tall guy and infer that he is good at basketball, an Asian and infer that she will be good at math. We meet a well-dressed person and infer he or she is successful. We think of the business we would like to start and infer it will be successful—because we ourselves desire what it will sell.

As we write, we make inferences as to what readers will make of what we are writing. We make inferences as to the clarity of what we are saying, what requires further explanation, what has to be exemplified or illustrated, and what does not. Many of our inferences are justified and reasonable, but some are not.

As always, an important part of critical thinking is the art of bringing what is subconscious in our thought to the level of conscious realization. This includes the skill of identifying and reconstructing the inferences we make so the various ways in which we shape our experiences through our inferences become more and more apparent to us. This skill enables us to separate our experiences into two categories. We learn to distinguish the raw data of our experience from our interpretations of those data, from the inferences we are making about them. Eventually we need to realize that the inferences we make are heavily influenced by our point of view and the assumptions we have made about people and situations. This puts us in the position of being able to broaden the scope of our outlook, to see situations from more than one point of view, and hence to become more open-minded.

Often different people make different inferences because they bring to situations different points of view. They see the data differently. To put it another way, they have different assumptions about what they see. For example, if two people see a man lying in a gutter, one might infer, "There's a drunken bum." The other might infer, "There's a man in need of help." These inferences are based on different assumptions about the conditions under which people end up in gutters, and these assumptions are connected to the point of view about people that each has formed. The first person assumes, "Only drunks are to be found in gutters." The second person assumes, "People lying in the gutter are in need of help."

The first person may have developed the point of view that people are fundamentally responsible for what happens to them and ought to be able to take care of themselves. The second may have developed the point of view that the problems people have are often caused by forces and events beyond their control. The reasoning of these two people, in terms of their inferences and assumptions, could be characterized in the following way:

Person One

Person Two

Situation: A man is lying in the gutter.

Situation: A man is lying in the gutter.

Inference: That man's a bum.

Inference: That man is in need of help.

Assumption: Only bums lie in gutters.

Assumption: Anyone lying in the gutter is in need of help.

As persons concerned with developing our thinking, we want to begin to notice the inferences we are making, the assumptions we are basing those inferences on, and the point of view about the world we are developing. To do this, we need lots of practice in noticing our inferences and then figuring the assumptions that lead to them.

Test the Idea
Distinguishing Between Information, Inferences, and Assumptions

As thinkers, it is important that we be able to distinguish among information, inferences, and assumptions. Whenever we are in a situation, we naturally make inferences. We come to conclusions about the situation or give it meaning through our interpretations. And these inferences result from the assumptions we made or are making.

For example:

  • If it were 12:00 noon, what might you infer? (It's time for lunch.)

  • If there are black clouds in the sky? (It's probably going to rain.)

  • If Jack comes to work with a black eye? (He was probably in a fight and hit by someone.)

  • If there are webs in the corners of the ceiling? (Spiders made them.)

  • If there is heavy traffic on the freeway? (I will probably be late for work).


  • If it were 12:00 noon and you inferred that it was time for lunch, what did you assume? (That whenever it is 12 noon, it is time for lunch.)

  • If there are black clouds in the sky and you infer that it's probably going to rain, what did you assume? (That it usually rains when there are black clouds in the sky.)

  • If Jack comes to work with a black eye and you infer that he must have been hit by someone, what did you assume? (That the only time you develop a black eye is when you have been hit by someone.)

In the following activity, we will provide you with situations (information). We want you to figure out what someone might infer (rightly or wrongly) in the situation. Usually there is a range of possible inferences that different people might make, depending on their various beliefs.

Then, having stated what you think someone might infer, figure out the assumption that would lead someone to make that inference. As a suggestion, first figure out a likely inference (whether rational or irrational), then, and only then, try to figure out the assumption. The assumption will be a generalization that led the person to make the inference. We have provided two examples to help you begin.


Possible Inference which one might make

Assumption Leading to the Inference

1. You see a woman in a wheelchair.

She must have a sad life.

All people in wheelchairs have a sad life.

2. A police officer trails your car closely for several blocks.

He is going to pull me over.

Whenever a police officer trails people he is going to pull them over.

3. You see a child crying next to her mother in the grocery story.


4. You do not get an increase in salary while others in your department do.


5. You meet a beautiful woman with blond hair.


6. You notice a man in the bookstore reading a book by Karl Marx.


7. While in a restaurant, your friend orders a steak cooked very rare.


8. A colleague tells you she is pregnant and is going to have an abortion.


9. Your teenage son comes home late from a late-night date.


10. Your spouse is talking to an attractive member of the opposite sex at a late night party.


11. The telephone rings in the middle of the night.


12. Your significant other does not call you when promised.


Our goal of becoming aware of the inferences we make and the assumptions that underlie our thinking enables us to begin to gain command over our thinking. Because all human thinking is inferential in nature, command of our thinking depends on command of the inferences embedded in it and thus of the assumptions that underlie it. Consider the way in which we plan and think our way through everyday events. We think of ourselves as preparing for breakfast, eating our breakfast, getting ready for work, arriving on time, attending meetings, completing necessary tasks, making plans for lunch, paying bills, engaging in small talk, and so on. Another way to put this is to say that we are continually interpreting our actions, giving them meanings, and making inferences about what is going on in our lives.

That is, we must choose among a variety of possible meanings. For example, am I "relaxing" or "wasting time"? Am I being "determined" or "stubborn"? Am I "joining" a conversation or "butting in"? Is someone "laughing with me" or "laughing at me"? Am I "helping a friend" or "being taken advantage of?" Every time we interpret our actions, every time we give them a meaning, we are making one or more inferences on the basis of one or more assumptions.

As humans, we continually make assumptions about ourselves, our jobs, our mates, our teachers, our parents, and the world in general. We take some things for granted simply because we can't question everything. Sometimes we take the wrong things for granted. For example, I run off to the store (assuming that I have enough money with me) and arrive to find that I have left my money at home. I assume that I have enough gas in the car only to find that I have run out of gas. I assume that an item marked down in price is a good buy only to find that it was marked up before it was marked down. I assume that it will not, or that it will, rain. I assume that my car will start when I turn the key and press the gas pedal. I assume that I mean well in my dealings with others.

We make hundreds of assumptions without knowing it—without thinking about it. Most of them are sound and justifiable. Some, however, are not. The question then becomes: "How can we begin to recognize the inferences we are making, the assumptions we are basing those inferences on, and the point of view, the perspective on the world that we are forming?"

As we become skilled in identifying our inferences and assumptions, we are in a good position to question the extent to which any one of our assumptions is justified. For example, are we justified in assuming that everyone eats lunch at 12:00 noon? Are we justified in assuming that it usually rains when there are black clouds in the sky? Are we justified in assuming that black eyes are only caused by someone hitting another person? The point is that we all make many assumptions as we go about our daily life and we ought to be able to recognize and question them. As you develop these critical intuitions, you should increasingly notice your inferences and those of others. You should increasingly notice what you and others are taking for granted. You should increasingly notice how your point of view shapes your experiences.

Test the Idea
Getting More Practice in Differentiating Inferences and Assumptions

Using the same format as we used in the previous activity, come up with 10 "episodes" of thinking for yourself, which include a situation, a possible inference in the situation, and the assumption leading to the inference.


Possible Inference one might make

Assumption Leading to the Inference





















Table of Contents, Thinking Tools Resources Page Previous Section, Thinking Tools Next Section, Thinking Tools