There is but one royal and straight road to the habit and power of thinking: reading. An education that does not form a reader is a stuccoed ignorance. Read every day. Do not read programmatically; do not read with a dictionary or a notebook or a commonplace book at your shoulder. Read as mood, interest, chance or caprice moves you. Programmatic reading relies on the memory of the programmer; but our memories of where ideas and notions first moved us tend to assimilate to their best expression, and we forget the survey or introduction, the passing reference, the awkward conversation which first inspired or illuminated us. The apostles of Literature are wont to forget that beneath the summit of Parnassus there is mountain to be scaled, with many approaches. Beware of anyone who says that to learn this, you must read this or that. Try what they say; but let your mind assert its own needs for corollary, introductory, or critical materials, for a fallowing break into some other subject (or into fiction), or for backtracking. The best minds, the most skilled, are often spoiled by prideful unwillingness to reconsider their assumptions and methods, to review the basics.
Never pause while reading to look something up. It is the first encounter which cuts the furrow, builds the pigeonhole, opens the file. If you get into the habit of pausing to look up, your mind will make such spaces only at the rate it can fill them from reference works; but if you let them open at the speed of uninterrupted reading they will be there to receive answers as they come to you in reading, conversation, walking on the proverbial heath—or in an apple orchard under the moon. Search for answers, and you find few; amass questions, and the world sings with answers. There are necessary exceptions: a chronology and maps are good to have to hand while reading history; and with foreign languages it is possible to be respectably skilled without being able to desert the dictionary. Too, there is no harm in noting topics for later investigation. But inertia should be your rule and your friend: finish what you start.
Never record notes or excerpts in the heat of the moment; finish a book before you extract from it. What is eloquent or moving in context may be dull or insipid when returned to directly; what seems essential or illuminating may be obvious later, or prove an oversimplification set as a snare for you by a careless or disingenuous author—textbooks are full of such intellectual mantraps. It is harmless to record a page or paragraph to return to; but as you are mortal, you must not waste time.
We remember what we learn more by the incidents of its acquisition than its place in a scheme. A book, as an article, is full of such incidents: binding, paper, cover and fonts; the author's style and voice; the circumstances where you read it; its weight on or in your hand; how you marked it or took pains not to mark or mar it; who you were when you read it; who gave to you or where you bought it or took it out; who recommended it; how old it is—new, secondhand, antique. A book is a mnemonically individual as a teacher and has the advantages of cheapness, reliable supply, permanence, and retainability—you cannot put a teacher on a shelf. Precisely because it is fixed and set, a book is not an indifferent medium (like the Internet) through which an item of data crosses from mind to mind; it is a physical thing, fraught and sensuous, whose circumstances receive and bind, like spiders' silk, gossamer and flighty thought. Love what books contain, but lust for books themselves; not with a gourmand's discrimination, but a voluptuary's delight.
The ancients, who had only fragile scrolls, and the scholars and schoolmen of the Middle Ages, who owned few books, built labyrinthine dream-palaces in their memories, full of niches and ramifying halls and galleries concocted from shards of remembered or imagined buildings. These palaces were miscellaneous as pattern books, like the strange buildings which haunt Renaissance backgrounds, D¨rer's rambling castles or the scenes where Poliphilo wandered; and which came as ruins to dominate Romantic landscapes, senseless conjunctions of towers and walls and columns; Death's city in Poe, resembling nothing which is ours. These palaces housed only commodious niches, ranged along hall walls or between arcade columns, or grouped behind doors: and in each niche, a vision lived—a nightmare, a fox-headed lady standing for a name beginning with V (vulpus); or a caricature, the goat with swollen testacles who was Cicero's testator.
But these were intimations. The true palace of memory is the library, with wings of shelves, corridors of volumes, niches of pages where memory is ensnared. The mind on its own holds but one palace; but there are books—classics—broad and deep enough to be palaces in themselves which one life cannot fill. So many counted light-years will not suffice to hold universe enough to justify, let alone satiate, the appetites and powers of the human mind; but books brought together do not add, but multiply; to be among books you know well is to be lifted out of mortal span and reach.