The phrase is said to have originated with Thomas Hobson (1544–1631), a livery stable owner in Cambridge, England, who offered customers the choice of either taking the horse in his stall nearest the door or taking none at all.
A Morton's fork is a specious piece of reasoning in which contradictory observations lead to the same conclusion. It is said to have originated with the collecting of taxes by John Morton, Archbishop of Canterbury in the late fifteenth century, who held that a someone living modestly must be saving money and therefore, could afford taxes, whereas those living extravagantly obviously were rich and could afford them as well.
In some instances, such as Morton's original use of the fallacy, it may be that one of the two observations is likely valid, but the other is pure sophistry: evidence of possessing wealth may be genuinely relevant to having a source of taxable income.
In other cases, it may be that neither observation may be relied upon to support the conclusion properly. For example, asserting that a person suspected of a crime who is acting nervously must have something to feel guilty about, while a person who acts calmly and confidently must be practiced or skilled at hiding guilt. Either observation therefore has little, if any, probative value, as equally, each could be evidence of the inverse situation.