One way to acquire a skill is to know consciously how to do every step (=explicit approach). With time, the procedure is automated. For traditional education it is typical to make sure students have as much of an explicit understanding as possible. The resulting knowledge should be automatic at some point (=implicit). However, it mostly doesn’t get that far. Why? Because taking explicit knowledge to the subconscious is a long, difficult way. Compared to the process of explicit knowledge acquisition, with implicit learning, the acquired knowledge is unconscious from the start.
Approaching a task explicitly from the start is not always the best way in order to arrive at an explicit understanding. Moreover, there is even the question whether explicit knowledge is needed at all.
For example, what we require of a football player is the ability to perform well, whether or not they understand why their performance is so good. A kid often knows how to play football even though it cannot verbally explain the rules of the game.
STIMULUS >> feel / react (implicit) >> think (explicit)
Explicit language learning
Learning word meanings might seem to be something that can be learnt explicitly quite easily – by dictionary definitions or translations. However, words can have subtle conditions on their use not captured by dictionary definitions. For example, the word ‘cause’ may seem to have the simple meaning ‘to bring about’. But the word is in fact largely used in contexts in which a negative rather than positive event has been brought about (one may ‘cause grief’ but it sounds slightly odd to ‘cause happiness’). This latter aspect of meaning is subtle and hence may not be noticed explicitly.
Learning grammar rules from the start often asks too much from a learner. People usually want to start understanding and speaking the language, rather than learning rules that make acquiring a language boring and frustrating. After all, the syntax of a language can readily be learned implicitly. So asking people to work out the structure consciously from the beginning might not be optimal.
Implicit language learning
Implicit learning is the acquisition of unconscious knowledge. This means that one learns to see the structural relations or syntax of a new language subliminally.
Rebuschat and Williams provided evidence that adults can learn aspects of a foreign language unconsciously. They presented participants (English mother tongue, target language German) with sentences composed with English words but German syntax (grammar) determining word order. Thus, the sentences were understandable to the participants, even if they sounded funny (‘Since his parents groceries needed, purchased David everything necessary’). On a later test, they were sensitive to rules of German syntax. People did not freely state any regularity relevant to key rules the participants were in fact sensitive to. That is, the rules could be acquired unconsciously.
First implicit, than – maybe – explicit
First it might be good to elaborate one’s intuitions. Afterwards, those intuitions may guide to an explicit understanding. In language learning, this would mean to start learning a new language intuitively. Without cramming vocabs. Without studying grammar rules by hard. After some time and with a “feeling” for the language (intuition through implicit learning), rules of the language may be learned explicitly. However, it is not of outmost importance in any stage of the learning process.
Learning advice: When learning a second language, make sure you listen and repeat sentences in real concrete contexts so that you soak up all the subtleties, even those which are not in grammar books, nor in dictionaries, nor even consciously noticed by yourself.
A language learning method incorporating implicit learning as the fundamentals is the Birkenbihl Approach. Linguajet offers computer/mobile language learning software based on this brain-friendly learning method.
 Rebuschat, P. & Williams, J. N. (2012). Implicit and explicit knowledge in second language acquisition. Studies in Second Language Acquisition, 33, 829–856.