If deception is the process of misleading others in order to get them to accept something as true even when it is false, then self-deception is the process of misleading yourself so that you will accept something as true even when you should acknowledge that it is false.
Not everyone agrees that self-deception exists, arguing that it is actually a contradiction in terms. For you to actually deceive someone, you must know the truth but then lead someone to believe the opposite. If you get someone to believe something which is false but were never aware that it was false, you cannot be accused of deception. You were wrong, but you werent deceiving anyone.
So, how can you possibly convince yourself of the truth of something if you already know it to be false? It seems more likely that that never really knew it was false, and instead fell victim to a process of confirmation bias and subjective validation which led you to believe something you probably shouldnt have accepted as true.
Although this objection makes a valid point, psychologists and sociologists who talk about self-deception reference the influence of unconscious motivations and prejudices. Thus, the process of self-deception represents a conflict between the conscious and unconscious portions of our minds. We may be faced with reasons that tell us that something is false, but the strength of our desires, biases, and prejudices work against us, causing us to develop the belief that it is true after all.
For example, a woman may be given clear proof that her husband has cheated on her with another woman but refuses to accept it, continuing in the belief that her husband has in fact been faithful. What exactly is going on in such a persons mind is difficult to understand, but it does seem clear that if anything qualifies as self-deception, then this would. Certainly she wants to believe that her husband is faithful and clearly she has a strong prejudice in favor of him, but this is conflicting with and evidently overcoming the evidence which her conscious mind is experiencing.
But what does she really believe and really know? She surely knows that the evidence against her husband exists and how strong it at least appears to be. Does she, however, actually believe that her husband is faithful? Or does she believe that he has cheated and is only saying that he hasnt? That simply isnt clear the conflict here is too difficult for us to disentangle the different issues.
Regardless of the exact process and situation, something similar to this happens far too often. Many, many people experience conflicts between what they would rather be true and what clear evidence informs them is true and, at least for a while, what they wish to be the case wins out over evidence, reason, and logic. This is much more than simple wishful thinking, however, because wishful thinking is often just a matter of rationalizing a poor situation, whereas self-deception involves adopting a position which has been clearly and unambiguously refuted. Very often, though, one melds into the other without clear boundaries.
Although the deception of others is typically regarded as a moral flaw, self-deception is usually treated as a reasoning flaw but is this a valid distinction to make? Perhaps if the idea you have deceived yourself into adopting has absolutely no repercussions for others then no moral questions are raised.
However, if this idea does have ramifications for others, then surely it cannot be treated as amoral. If you have a genuine and honest belief that your dog is safe which was developed through self-deception, and then later your dog attacks a neighbor, cant we conclude that your self-deception was unethical?
It should be kept in mind, of course, that not every apparent act of self-deception really does qualify. There may be good reasons for a person to distrust apparently sound evidence and what we treat as bias or prejudice may not be playing a role after all. The problem here is that an accusation of self-deception usually hinges upon the existence of particular motivations motivations which are likely unconscious to the person in question.
To what degree can we count ourselves qualified to evaluate and discern such motives and biases? If you have training and experience with psychological evaluations and you are speaking about a person with whom you have a great deal of experience, then perhaps your conclusions can be trusted. Otherwise, an accusation of self-deception should be made with only the greatest of care, if at all.