Thus are explained "errors of the senses," which are in reality errors of interpretation. Thus too, and in the same manner, we have the explanation of dreams.
Let us take a simple example. When you read a book, do you spell each syllable, one by one, to group the syllables afterwards into words, and the words into phrases, thus travelling from print to meaning? Not at all: you grasp a few letters accurately, a few downstrokes in their graphical outline; then you guess the remainder, travelling in the reverse direction, from a probable meaning to the print which you are interpreting. This is what causes mistakes in reading, and the well-known difficulty in seeing printing errors.
This observation is confirmed by curious experiments. Write some everyday phrase or other on a blackboard; let there be a few intentional mistakes here and there, a letter or two altered, or left out. Place the words in a dark room in front of a person who, of course, does not know what has been written. Then turn on the light without allowing the observer sufficient time to spell the writing.
In spite of this, he will in most cases read the entire phrase, without hesitation or difficulty.
He has restored what was missing, or corrected what was at fault.
Now, ask him what letters he is certain he saw, and you will find he will tell you an omitted or altered letter as well as a letter actually written.
The observer then thinks he sees in broad light a letter which is not there, if that letter, in virtue of the general sense, ought to appear in the phrase. But you can go further, and vary the experiment.
Suppose we write the word "tumult" correctly. After doing so, to direct the memory of the observer into a certain trend of recollection, call out in his ear, during the short time the light is turned on, another word of different meaning, for example, the word "railway."
The observer will read "tunnel"; that is to say, a word, the graphical outline of which is like that of the written word, but connected in sense with the order of recollection called up.
In this mistake in reading, as in the spontaneous correction of the previous experiment, we see very clearly that perception is always the fulfilment of guesswork.