Although we talk about 'learning' to talk and 'learning' to walk, we probably recognize that the process is very different to 'learning' to ride a bike or 'learning' history. Walking and talking seem to 'just happen'. We do not intend them to happen; most of the time we are unaware that they are happening; we cannot really explain what is involved. Learning to ride a bike or learning history, on the other hand, requires intention, and usually explicit learning: they are generally taught, and not instinctively 'acquired'. So what explanations have been offered to explain subconscious, implicit language acquisition?