These words refer to uncertain or unsteady speech. Stutter is the most concrete and technical of these, referring to a chronic speech defect in which there is spasmodic repetition, blocking, prolongation of sounds and syllables, especially of initial ones; such a defect may have an organic or physiological element, but is mainly caused by a psychological disruption of normal development: therapeutic and remedial training for children who stutter . Stammer may suggest a milder degree of speech difficulty, such as halting speech, or it may apply more widely to any temporary or momentary difficulty in speaking that stems from shyness, uncertainty or any excess of emotion: blushing and stammering under the attractive man’s searching glance; stammering that he didn’t know where he had put his keys; finally able to stammer out how much she loved him. Sometimes the word can be used in a euphemistic way to replace what may be thought of as the harsh directness of stutter : assuring him that many a child stammered a bit and that it would go away if he didn’t think about it.

Whereas the previous pair emphasize an involuntary difficulty, hem (which is rare) and hum and haw more often suggest a deliberate reluctance to state something directly. Thus, while the words can suggest the embarrassed or halting manner of stammer , they more often point to someone trying to avoid answering a question or buying time until the right reply occurs to him: a question that was so surprising that he could only hum and haw in answer. As the amount of suggested evasiveness increases, hum and haw can point also to someone who speaks in a slow but more particularly a roundabout or evasive manner: humming and hawing about generalities instead of explaining the statistics I had cited. Stumble is more like stammer in suggesting a temporarily halting speech that is involuntary: stumbling over his words in his haste to tell the whole story. The reason here may be the same as for stammer ; but the word can once or twice in a very long speech.