Lesson 2
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Quick Quiz on Inference

Inference

It is important to distinguish between observations and inferences. The colors and color changes, the temperature and temperature changes, the smells that you may come across in this lesson and throughout this course are directly observed and they can be classified as observations. When you do something with that observation, like draw a conclusion or offer an explanation or decide that a chemical reaction occurred, then you are making an inference. The inference may or may not be a correct one. Correctness is not what makes the difference between observation and inference.

An observation is the awareness of some condition; inference is the result of a mental process which attempts to explain or catalog or speculate about that observation. So far we have had several examples of observations (and measurements as well), but we have not really talked about inferences. A few examples might help to illustrate the point.

Cloud [1infclo.jpg (25377 bytes)] In this picture, you can observe that there is some white material up in the air. One of the inferences that you might make is that you are looking at the picture of a cloud. Another inference you might make is that there was a brush fire in the direction that the the picture was taken, or perhaps Mt. St. Helens has erupted again after all these years. Whether or not any of those statements is true is beside the point at the moment. Saying that it is a picture of a cloud is an inference. Observing the white stuff behind the trees and building is the observation.

There are times when observations and inferences are very much intertwined with one another and then it can be very difficult to make the distinction. This is because observation and inference both are mental processes. An example of this is a mirage or an optical illusion.

Mirage [1infmir.JPG (7860 bytes)] If you have ever seen the light shimmering off the road or countryside out in the desert, it looks like water. That is an inference. What you are observing is the reflection of the light, and you are inferring that it is reflecting off water.

Optical illusion with tabletops [1inftab.JPG (4628 bytes)]Here is another possible example of an optical illusion. In this diagram of two tabletops submitted to the April 1998 issue of "The Physics Teacher" by Martin Gardner, you have probably inferred that the tabletop on the left is longer than the tabletop on the right. If you were to make a copy of this diagram from the original article and superimpose the two you would find that they are the same size and shape. (The display on the screen and on your printer may be slightly distorted.) Your inference seems to be an observation, but it is not. However, your mind is making the inference at such a basic level that it appears to be an observation.

Yelow and blue overlapping lines [inf-ybg.gif (1852 bytes)]In the diagrams shown here the closely spaced blue and yellow lines take on a different appearance where they overlap. Indeed, the white portions of the screen background that you are looking at is not really white, but rather closely spaced blue, green and red dots that your brain has blended together and interpreted as white.

So, observations and inferences are sometimes a bit hard to distinguish from one another. But for the most part, if you are careful about making the distinction, at least in this course, you won't have too much trouble figuring out what is an observation and what is an inference. Making inferences involves knowing how to look beyond what you actually observe, and to know that you are doing it. Remember that the point here is not that observations are correct and inferences are incorrect, but rather that there is a difference and that you need to know what that difference is.