We once thought that vocabulary was almost all acquired incidentally through encounters with words in conversation and in texts. Indeed, many words can be acquired incidentally. However, the learners who do the best job of acquiring new words this way are those who already possess a broad vocabulary. Especially for learners who have sparse vocabulary knowledge and who need to learn many words quickly in order to catch up, explicit teaching of some carefully chosen words can be very productive and efficient.

Incidental word learning depends on the learner’s capacity to derive meaning from context.  Sometimes we can do this from a single exposure.  For example, compare the following sentences:  

Cleopatra’s subjects were amazed at her pulchritude.  

Cleopatra was popular because of her beauty; her subjects commented approvingly on her pulchritude. 

In the first case, many interpretations of the word are possible: power, money, intelligence, stupidity, shyness, dancing ability, even wardrobe could all be filled in for pulchritude.  In the second sentence, it is possible to figure out that pulchritude means beauty.  Unfortunately, sentences of the second sort are much less likely to occur in texts, so the efficiency of incidental learning is fairly low.  Furthermore, incidental learning even from sentences like the second example is possible only for those students who understand the rest of the sentence.  So again, the most advanced students do a better job of inferring the meaning of new words from context than the students who most need new vocabulary.  

Perhaps the most common approach to vocabulary instruction is to ask students to look words up in the dictionary.  Dictionary definitions can be an important tool as part of vocabulary instruction but, taken alone, they rarely provide meanings sufficiently rich to support adequate learning.  In 1974 George Miller studied sentences children had produced after studying dictionary definitions for novel words.  The sentences showed clearly that dictionary definitions give students rather limited and sometimes incorrect information about word meaning. For example:

The dishes come out of the dishwasher chaste.

This is not to say that using dictionaries is a bad idea. While dictionaries can be very helpful in confirming or refuting guesses about word meanings, they must be used in conjunction with other sources of information.

Too often, students are expected to comprehend texts containing many unfamiliar terms. We agree that it is not necessary for students to know every word in a text—and we recognize that one way to learn new words is to encounter them in print. But possessing the capacity to learn unfamiliar words requires a student to know almost all the other words in the text. Indeed, if students don’t know at least 95% of the words in a text, comprehension of the main points is likely to be inadequate. Without comprehending the text, students are unlikely to learn any of the unfamiliar words. In other words, when we want to rely on providing students with texts as a resource in vocabulary learning, we need to be very careful to select texts that offer just the right level of challenge. For students who are functioning far below expectations, such texts might be very simple and may not offer exposure to the words needed for grade-level work.

Word learning seems remarkably fast and efficient, so teachers sometimes conclude that a word that has been taught will have been learned. But in fact, words are typically learned only after several exposures. Of course, something about the word might be learned from the first exposure – perhaps whether it is a noun or a verb, or some vague idea of what it means. But subsequent exposures are needed to nail down the meaning, to fully understand exactly how the word is used, and to be sure it is remembered. Thus, effective vocabulary instruction requires built-in opportunities for learners to hear or read target words several times over the course of a few weeks. 

Think of words that most three-year-olds know—dog, spoon, table, run, eat.  These are simple words, typically learned during daily interactions between parents and toddlers, e.g: the book is on the table; you dropped your spoon; eat your peas!  And we gladly give the three-year-old credit for knowing those words when they label dogs and tables, or say things like ‘wanna run’ or ‘mommy eat it.’  But knowing even these simple words well enough to understand them in advanced texts requires much more than the three-year-old knows.  Consider sentences like the following:  

            His problems continued to dog him.

            They spooned up to keep warm.
 
            Let’s table the motion and consider it tomorrow.

            He ran the experiment as soon as the conditions were right.

            The comptroller found a way to eat the expenses.  

Most words, like these five, actually have many closely related meanings, and when such words are used in academic discourse or in writing they often carry meanings that are uncommon and unfamiliar to young children.

Many of us have our favorite techniques for learning or teaching word meaning.  Some of us learn words by discovering them in crossword puzzles or dictionaries.  Others learn them from reading a lot.  Others have a feel for the morphological variations in words, and thus can make good guesses about what complex forms mean.  Still others know enough Spanish or Latin or Greek or German to be able to make reasonable guesses about the meanings of words using etymology.  All these routes to word knowledge are valuable, and yet none alone is sufficient to ensure rapid acquisition.  When we are designing vocabulary curricula, we need to be sure that a variety of strategies are taught and implemented whenever possible.  

Cognates, particular Latin-based words likely to have similar forms in Spanish, can be a good source of reasonable guesses about word meaning.  Unfortunately, teachers often worry much more about the tiny proportion of cognates that are ‘false’ (i.e., the meanings in Spanish and English are not the same) than about the vast majority of cognates where meanings are very similar.  Even many false cognates (e.g., the commonly cited embarazada and embarrassed) in fact are etymologically related, though the meanings in Spanish and English have drifted enough apart that the sense of being burdened now signifies pregnant in Spanish and abashed in English.   

In general, of course, the words we worry that students should learn are the less frequent ones, the ones least likely to be used in spoken language.  But it is important to realize that some of those less frequently used words are weightier and more crucial in expressing distinctions in meaning than others.  Some rare words, like the example pulchritude cited earlier, are nice to know for spelling bees, but are rarely encountered in key positions in text.  One set of very important words includes the words used to talk about truth, evidence, and drawing conclusions.  These include verbs like affirm, deny, confirm, suggest, support, prove, and doubt, nouns like evidence, claim, theory, hypothesis, assertion, argument, proof, and expressions like call into question, cast aspersions on, relate to, and conform with.  These are words that are likely to be encountered in math, science, and social studies texts, though with slightly different meanings in those different contexts.  They are crucial in understanding the kinds of information presented in textbooks.  

Another set of words that is very helpful in talking about truth, claims, and conclusions are words that signal relations between sentences.  Some of these discourse connectives are quite frequent, simple at least in their core meaning, and get learned incidentally, e.g., and, then, so, but.  Others are less frequent, more complex in meaning, and often skipped over by less skilled readers, yet if noticed and understood they can be very helpful in structuring comprehension of a text.  This list includes words like unless, although, despite, thus, nonetheless, and however.  Some strategic, explicit teaching of this small set of terms is likely to help students enormously.

Very often vocabulary instruction relies on students selecting the words they don’t know from a text.  While self-identified words should certainly be attended to in vocabulary instruction, we should not be fooled into thinking that poorer readers always recognize which words they don’t know. First, students may know a word in its simplest meaning but not comprehend the more specialized meanings that could be associated with a particular text. Second, many words seem familiar; unless students are doing a good job of monitoring their comprehension, they may not even realize that they don’t fully understand what particular words mean.  

Knowing how to pronounce words suggests that students have encountered them before, and knowing how to spell them is certainly important.  However, these aspects of word knowledge can be acquired without much attention to meaning.  Correct pronunciation and spelling should be seen as ways to consolidate knowledge about words and to ensure they can be easily recognized and retrieved; however, knowing about meaning and use is much more important than simply pronouncing a word correctly when it is encountered in print.