The general rule is, that when two sounds come together, those movements of articulation which are common to both are executed once only. Thus in don't,[64] the stopping of the passage for [n] also does duty for [t]; it is the opening of the passage which constitutes the [t]. In stamp the closure for [m] also does duty for [p]. In witness the closure for [t] remains for [n], which merely requires the opening of the nose-passage and vibration of the vocal chords.
Utter the word clean, and observe whether you produce the [k] in the same way as in keen; probably you will find that for the [k] of clean you open the closure only at the sides, leaving the centre of the tongue in contact, ready for the production of [l]. See whether anything similar happens when you say the word atlas.
Sometimes a voiced sound makes a neighbouring sound voiced, or a voiceless sound makes a neighbouring sound voiceless. Examples in the nursery rime are [bəːdzz̥] and [beikt]; find similar examples of the s of the plural[65] and the ed of the past participle, and determine in each case whether the final sound is voiced or voiceless. Try to find pairs like lagged and lacked, bids and bits.
Utter the words apt, act, and notice carefully when you make the closure for [t]; probably it is earlier than you would have thought. Do you make the [n] closure in open before or after the [p] opening?
In compound words, and in neighbouring words which belong closely together, assimilation is common. When one word ends in a voiceless sound and the other begins with a voiced sound, or vice versa, it is usually the second which prevails. Observe cupboard [kʌbəd], raspberry [rɑːzbəri], blackguard [blægɑːd], bedtime [betaim], hold tight [houltait].
Consider the pronunciation of observe, obstacle, gooseberry, absolve, absolute.
In careless speech [hɔːʃu] is heard for [hɔːsʃu], [lædbru grouv] does duty for Ladbroke Grove, and [həsijn] for has seen. Is she is regularly pronounced [iʒ ʃi], or [iʃi] in quick conversation.
The nasals frequently change to suit the place of articulation of the following sound, as in congress [kɔŋres], congregation [kɔŋri´geiʃən], anchor, concave, conclusion, concourse, concrete, syncope, tranquil, unctuous, pincushion [piŋkuʃən], infamous [imfəməs], Holland Park [hɔləmpɑːk]; or of the preceding sound, as in second single [sekŋsiŋgəl], captain [kæpm̩], open the door [oupm̩ ðə dɔː], cup and saucer [kʌpm̩sɔːsə]. The examples from pincushion onwards occur only in distinctly careless speech.
The change of to [z] in house, houses [haus, hauziz], shows a different kind of assimilation.
50. The dropping of d in four-and-twenty might also be due to the desire to simplify a group of consonants; and this will seem the more likely explanation if we notice that the d of and is generally dropped before a consonant, but kept before a vowel. Compare you and Ida, bread and butter; if you drop the d in the first instance, or utter it in the second, you are equally wrong. Such simplifying is fairly common in educated speech; most people drop the t in often, and the p in empty (where it has no etymological justification), and jumped; in colloquial speech don't know is [dʌnou]. In quite careless speech you may notice consonants dropped in such words as acts, insects, but this is clearly a licence which cannot be permitted in the class-room. Indeed these groups of consonants should be articulated with great care. Nothing so quickly gives an effect of slovenly speech as the slurring of consonants, where it is not generally adopted.