What is Wishful thinking fallacy?

While many of us engage quite happily in wishful thinking, we elevate it to the status of a fallacy when we use it in place of argument. If we accept a contention because we would like it to be true, rather than because of the arguments or evidence which support it, we move into fallacy. Similarly, we also commit the fallacy of wishful thinking if we reject something solely because we do not wish it to be true.

Going to work in this awful weather would do no good for anyone. I think I'll take the day off and stay in bed.
(Everyone must have felt the force of this argument at some time. Unfortunately, while there may be reasons for and against going into work, not wanting to is one which lacks persuasive force over everyone except ourselves.)

Our wishes rarely bear directly on the question of whether a thing is true or false. We commit a fallacy by intruding them into a discussion of the pros and cons. To suppose that the world is as we would want it to be is good solipsism but bad logic.

Of course the environment talks will succeed. Otherwise it means man-kind is on the way out.
(The fact that we want them to succeed does not mean that they will. It could be that mankind is on the way out; in which case you might just as well be packing as hoping.)

Wishful thinking often appears to colour our judgement of outcomes we are unable to influence.

He can't die. We couldn't manage without him.
(He did. They could.)

Death, in fact, is a subject especially prone to the fallacy of wishful thinking. Its abrupt and inconsiderate nature is softened by the fallacy into something we would find more acceptable, although our wishes hardly afford valid grounds for our supposition. Boswell, on a visit to the dying Hume, asked the philosopher about a possible afterlife:

Would it not be agreeable to have hopes of seeing our friends again?
(He mentioned three recently deceased friends of Hume, but the latter firmly rejected the fallacy. 'He owned it would be agreeable', Boswell reported, 'but added that none of them entertained so absurd a notion.')

Time, like death, is a field in which our wishes replace our ability to influence.

It can't be Friday already! I've not done nearly enough work to pass the exam!
(Wrong about the day; right about the exam.)

The problem about all wishful thinking is that if you want one thing and the laws of the universe dictate another there is a conflict of interests which is not going to be resolved in your favour. This being true, you might as well spend time working out how to deal with the outcome, instead of wishing that something else would happen.

The bank will extend our overdraft; otherwise we just cannot survive.
(Bank managers are not interested in your survival. They care about only two things: making money for the bank and grinding the faces of the poor.)

Most of us are already fairly adept at using the fallacy of wishful thinking to persuade ourselves. When using it to con-vince others, bear in mind that it must be their wishes, rather than your own, which are appealed to.

The business will succeed. You'll get a huge return on your investment.
(This is more effective than 'The business will succeed. I'll be rich for life!')