Distinguishing Between Inferences and Assumptions
To be skilled in critical thinking is to be able to take one’s thinking apart systematically, to analyze each part,
assess it for quality and then improve it. The first step in this process is understanding the parts of thinking, or
elements of reasoning.
These elements are: purpose, question, information, inference, assumption, point of view, concepts, and
implications. They are present in the mind whenever we reason. To take command of our thinking, we need to
formulate both our purpose and the question at issue clearly. We need to use information in our thinking that
is both relevant to the question we are dealing with, and accurate. We need to make logical inferences based
on sound assumptions. We need to understand our own point of view and fully consider other relevant
viewpoints. We need to use concepts justifiably and follow out the implications of decisions we are
considering. (For an elaboration of the Elements of Reasoning, see a Miniature Guide to the Foundations of
In this article we focus on two of the elements of reasoning: inferences and assumptions. Learning to
distinguish inferences from assumptions is an important intellectual skill. 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 we believe that it is dangerous to walk late at
night in big cities and we are staying in Chicago, we will infer that it is dangerous to go for a walk late at
night. We take for granted our belief that it is dangerous to walk late at night in big cities. If our belief
is a sound one, our assumption is sound. If our belief is not sound, our 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 he makes it only when he 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.
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 inferences. 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 upset. 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 read a book, and interpret what the various
sentences and paragraphs — indeed what the whole book — is saying. We listen to what people say and make
a series of inferences as to what they mean.
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 recognition that our experiences are shaped by the
inferences we make during those experiences. It enables us to separate our experiences into two categories:
the raw data of our experience in contrast with our interpretations of those data, or 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 viewpoints. They
see the data differently. To put it another way, they make 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. Moreover, these assumptions are connected to each
person’s viewpoint about people. 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 care for 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
Situation: A man is lying in the gutter.
Inference: That man’s a bum.
Assumption: Only bums lie in gutters.
Situation: A man is lying in the gutter.
Inference: That man is in need of help.
Assumption: Anyone lying in the gutter is in need of help.
Critical thinkers notice the inferences they are making, the assumptions upon which they are basing those
inferences, and the point of view about the world they are developing. To develop these skills, students need
practice in noticing their inferences and then figuring the assumptions that lead to them.
As humans, we continually make assumptions about ourselves, our jobs, our mates, our students, our
children, 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
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.
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