Sentences may be reduced to component parts; sometimes these are words, but quite as often they are word-groups (such as compounds and phrases) or units less than words (such as affixes).
The word, not the sentence, is the basis of translation. Since a word has a definite meaning and conveys a definite idea it is easy to find the foreign equivalent.
A sentence has generally, if not always, a definite foreign equivalent. A word is so unstable that it may entirely change its meaning when used with other words.
It is easy to memorize words and difficult to memorize sentences.
It is as easy to memorize a six-word sentence as six words.
If we learn a few dozen words we can build up thousands of sentences from these by the synthetic process.
If we learn a few dozen sentences we can construct thousands of others from these by disintegration and substitution, and, what is more, we can recognize them and use them even in rapid speech.
The collection of word-families is a valuable way of enriching one's vocabulary.
The enriching of one's vocabulary should be left to a comparatively late stage in the study of language, especially in the study of most derivatives and compounds.
Words constitute the 'primary matter' (_i.e._ matter to be memorized integrally without analysis or synthesis). Sentences constitute the 'secondary matter' (i.e. matter to be derived synthetically from primary matter).
It is precisely because sentences are so rarely considered as 'memorized matter' that so few people manage to understand the foreign language when spoken or to express themselves correctly in it.
Take care of the words and the sentences will take care of themselves.
Take care of the sentences and the words will take care of themselves.
_Should irregularities be included or excluded during the earlier stages?_
The regular is easy, the irregular is difficult; in the interest of gradation let us therefore exclude temporarily the irregular.
Irregular forms are generally more used and more useful than regular ones; in the interest of gradation let us therefore include all necessary irregularities even in the earlier stages.
Irregular forms make it difficult to formulate precise rules.
Rules with numerous exceptions are not worth formulating at all.