What is Unaccepted enthyrnemes fallacy?

An enthymeme is an argument with one of its stages understood rather than stated. This is all right as long as both parties accept the tacit assumption. When the unstated element is not accep-ted, we move into the territory of the fallacy.

Bill must be stupid. You have to be stupid to fail a driving-test.
(While the average listener might nod sagely at this point, he would be somewhat put out if he later discovered that Bill hadn't failed his driving test. The argument only works if that is assumed.)

In this case a fallacy is committed because an important element of the argument is omitted. If both parties agree on the assumption, then it is present although unstated. If only the lis-tener makes the assumption, he may think the argument has more support that it really does. We often leave out important stages because they are generally understood, but we have to recognize that there can be disagreements about what we are entitled to assume.

I hope to repay the bank soon, Mr Smith. My late aunt said she would leave a reward to everyone who had looked after her.
(The bank manager, surprised by the non-payment of the debt, will be even more surprised when you tell him how you had always neglected your aunt.)

It is because we use enthymemes routinely to avoid labor-iously filling in the details that opportunities for the fallacy arise. The earnest caller who wishes to discuss the Bible with you will be satisfied if told ‘I’m a Buddhist’, because both parties accept the implicit fact that Buddhists do not discuss the Bible. If, however, you were to reply instead: ‘Buddhists don’t discuss the Bible’, your caller might still be satisfied, making the obvious assumption that you were a Buddhist. (Make sure though that you have a very good answer ready should you happen to meet him in church next Sunday.)
Unaccepted enthymemes form ready crutches for lame excuses. The listener will generously clothe them with the unstated part necessary to complete the argument, instead of leaving them to blush naked.

Darling, I'm sorry. Busy people tend to forget such things as anniversaries.
(This is fine until your colleagues mention that you've done nothing for two months except the Telegraph crossword.)

The fallacy is easy to use, and will get you off the hook in a wide variety of situations. The procedure is simple. Give a general statement as the answer to an individual situation. Your audience will automatically assume the missing premise: that the general situation applies to this particular case. What people normally do in certain circumstances is only relevant to the charges against you if it is assumed that you were indeed in those circumstances. The unaccepted enthymeme will slide in as smoothly as vintage port.

Yes, I am rather late. One simply cannot depend on buses and trains any more.
(True, but you walked from just around the corner.)

You can equally well make general assertions during a discussion about someone in particular. Your audience’s delight at gossip and determination to believe the worst in everyone will help the unaccepted enthymeme to mingle with the invited guests.

I'm not happy with the choice of Smith. One can never be happy with those who prey on rich widows.
(Or on unjustified implications.)