Assumption versus Inference

In my books and my speaking, I often refer to assumptions and inferences. On the surface, these two things seem to be identical, but there are some subtle differences. Today I’d like to clarify what they are.

An assumption is something we take for granted or presuppose. In the teaching profession, for example, too many teachers assume that students know what the teacher wants the students to do—without the teacher actually teaching how to do it. Likewise, parents may assume that it is important for their children to get good grades in school. But their children may not have the same assumption. Good grades are important to some students but not for all. Or, a wife may assume that her husband knows the answer when he asks, “Are you going on a walk with me after dinner?” And the wife says, “I went for a walk this morning.”

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

However, in the examples above, there is no significant difference between an assumption and an inference. In most cases, the difference depends on the situation. The following example will help clarify the difference.

A man is lying in the gutter.

Assumption: Only bums lie in gutters.
Inference: Anyone lying in the gutter is in need of help.

Assumption: That man is a bum.
Inference: That man is in need of help.

Ultimately, these terms will always be fuzzy because in most cases it depends on the circumstance.