In Dutch as well as in English, there are quite a number of words that have a particular pronunciation when said in isolation (called the strong form or SF), but, except when they occur in certain positions, have a different pronunciation when they are used in connected speech (called the weak form or WF). Such words are called gradation words, gradation being the technical term for the reduction of strong forms to weak forms.
Consider the English example He has told us, in which three of the four words are gradation words. In this sentence, WFs are used: /hi z toʊld əs/, but in isolation they would have their SFs: /hiː/, /hæz/, and /ʌs/. It will appear in the sections below that GA gradation words typically lose initial /h/ and /w/, and that vowels, when not actually elided, are reduced to /ə/, or to weak /i/ and /u/.
In general, learners tend to use too many SFs, which may make their pronunciation sound unnecessarily formal, or even a little pompous. Despite the fact that the two languages share this feature, the use of WFs in English must still be learned and practiced because (i) words whose Dutch equivalents have noWFs may have WFs in English, or vice versa, and (ii) the form of the English WFs may be different from what might be expected on the basis of their Dutch equivalents. In addition to this, you should remember that when reading out a text, and certainly when reading a text in a foreign language, people generally have an inclination to pronounce SFs where WFs should be used. In order to read texts naturally and competently, you should make a point of using WFs where appropriate. Also, to turn to the perception aspect of this, you may discover that you do not spot WFs in the colloquial pronunciation of native speakers. Dutch speakers often fail to hear /d/ in He’d like to go, I’d rather not, etc., or /ðət/ in I know that John is right, etc.
Gradation words are always function words. In particular, they belong to the following word classes: the articles (lidwoorden), pronouns (voornaamwoorden), auxiliaries (hulpwerkwoorden), prepositions (voorzetsels), conjunctions (voegwoorden). In contrast, major-class words are never gradation words. Major classes are lexical verbs (hoofdwerkwoorden), nouns (zelfstandige naamwoorden), adjectives (bijvoeglijke naamwoorden), and adverbs (bijwoorden).