An inappropriate use of the word 'therefore' or 'so' to persuade listeners or readers that something has been proved when in fact is hasn't. The words 'therefore'and 'so' are usually used to indicate that what follows is the conclusion of an argument, either explicitly stated or implied. For instance, in the following argument, the word 'therefore' is used correctly to indicate that what follows is a conclusion derived from the given premises by means of deduction:
All fish live in water
Socrates is a fish
Therefore Socrates lives in water.
The word 'so' could equally well have been used in place of 'therefore'. In everyday speech it is often tedious and unnecessary to spell out all the premises of an argument, since it is usually reasonable to assume that the person with whom we are talking shares many of our assumptions. We would probably be inclined to say something like: 'Socrates is a fish, so of course he lives in water', rather than give the full argument as above. This is an enthymeme, an argument with a suppressed premise (that all fish live in water). There is nothing wrong with this provided that it is clear what has been left out.
However, some writers and speakers exploit the persuasive power of 'therefore' and 'so', and liberally sprinkle their prose with these words, even though they do not offer any argument for their would-be conclusions (eg, most of JCanons threads). This is an easy alternative to arguing for your conclusions and many casual readers are taken in by it. But in fact the supposed conclusions which follow spurious uses of 'therefore' and 'so' are non sequiturs. For instance, if someone says 'Boxing often causes brain damage, so it should be banned', the conclusion which follows 'so' could have been derived from several different suppressed premises, such as 'Any activity which often causes brain damage should be banned' or 'Sports which often cause brain damage should be banned', or 'If boxing often causes brain damage then it should be banned',. This list does not exhaust the possible alternatives. But unless the premise is obvious in the context, or else actually stated, the use of 'so' is spurious: it gives the superficial appearance of an argument, but in fact is merely a disguised assertion. It is either a case of sloppy thinking, or else an attempt to persuade by means of a rhetorical device.
(from 'Thinking from A to Z' by Nigel Warburton - 2nd edition)