user-1: His, Dogen's, Fukanzazengi, says

Think of not-thinking. How do you think of not-thinking? Be before
  thinking. These are the basics of zazen.

I haven't, I think, been formally taught zazen. But how does this sound, as a paraphrase:

think of thinking which is no longer thought

Because, taken literally, I feel that it is a very good way of looking at our relationship to history, when we cannot do anything about it.

user254: To me the English phrase, "think of thinking which is no longer thought" implies that it used to be thought, that it was previously thought, but is no longer thought i.e. it is not thought any more. In other words it's something to do with after thought, not before thought.
The way I understand "before thought" is, for example, if I see a tree then what I'm seeing is light reflected off a tree: I'm seeing light after it's reflected (instead of seeing the tree itself). If I wanted to know the tree (i.e. reality) and not just know the reflected light (i.e. thoughts), then I ought to consider what's happening before the light is reflected.

user8238: I had a look at translations of Dogen's essay "Universally Recommended
Instructions for Zazen":

Think of not thinking. Not thinking-what kind of thinking is that?
  Nonthinking. This is the essential art of zazen.

https://web.stanford.edu/group/scbs/sztp3/translations/gongyo_seiten/translations/part_3/fukan_zazengi.html
I did further research on the text and came across the archaic Japanese original as well as the modern Japanese translation.
Dogen's Original Passage

箇（こ）の不思量底を思量せよ。不思量底、如何（いかん）が思量せん。非思量。これ乃（すなわ）ち坐禅の要術なり。

Modern Japanese

不思量に止（とど）まり居る処のみを任運に、そのまま不思量底であるところ、本来の相としての非思量に在る。これが、まさに坐禅の要術である。

http://www.geocities.jp/sybrma/235.5hukanzazengi.yaku2.html
Now I am not a Japanese speaker, however the Chinese characters (Kanji) used in both passage are 不思量 and 非思量 which would roughly translates as 'not thinking' and 'non thinking'. Suggesting that 'be before thinking' is not a good translation.
Further research indicates the context that the phrase was used:

These words appear in a dialogue that Dogen makes the subject of SBGZ
  Zazenshin: A monk asked Yueh-shan, "What does one think of when
  sitting motionlessly in zanen?" Yueh-shan replied, "You think of
  not-thinking." "How do you think of not-thinking?" asked the monk.
  "Nonthinking," answered Yueh-shan.

http://www.sunypress.edu/pdf/60478.pdf
This would suggest that the intent of his message was not about some kind of 'prescience' (the fact of knowing something before it takes place; foreknowledge) as the word be before thinking or before thought would suggest, but the single pointed concentration that result in the falling away of thoughts.
This corresponds with the mental factors of the Jhana, which the the Pali root word for Chan/ Zen.

First Jhāna — the five hindrances have completely disappeared and
  intense unified bliss remains. Only the subtlest of mental movement
  remains, perceivable in its absence by those who have entered the
  second jhāna. The ability to form unwholesome intentions ceases. The
  remaining qualities are: "directed thought, evaluation, rapture,
  pleasure, unification of mind, contact, feeling, perception,
  intention, consciousness, desire, decision, persistence, mindfulness,
  equanimity & attention"
Second Jhāna — all mental movement utterly ceases. There is only
  bliss. The ability to form wholesome intentions ceases as well. The
  remaining qualities are: "internal assurance, rapture, pleasure,
  unification of mind, contact, feeling, perception, intention,
  consciousness, desire, decision, persistence, mindfulness, equanimity,
  & attention"

As noted, by the second Jhana all thoughts have ceased, only awareness of bliss and other Jhanic factors remains.
A poster here suggested that it could be to do with:

When one's perceptional faculties are acutely developed and on the
  cusp of awakening, logical perception will begin to occur before
  emotional perception.

While this could possibly occur in meditation, it is not suggested in the actual text. Further more, given that the text was meant to be a universal recommendation, it would imply that the text was directed at general audiences, who do not have the necessary background in meditation. Who might be wondering what they are supposed to think during sitting meditation, the answer being not think of anything in particular. (A more systematic way is to direct your thoughts to an object of focus, for example your breathing).

user715: 
Think of not-thinking. How do you think of not-thinking? Be before thinking. These are the basics of zazen.

When one's perceptional faculties are acutely developed and on the cusp of awakening, logical perception will begin to occur before emotional perception.
For example, if there is a loud bang, the first perception in the mind will be, just a loud bang, nothing to fear. The very next nano second, the emotional perception will arise, suggesting fear and panic. However this emotional message will have no relevance because the event has already been cognized logically.
In modern scientific terms, one could describe it as the speeding up of the logical brain over the pre-brain. 
By intently examining every moment in zazen we cause the evolution of the response time of the brain's logical faculties. 
To be before thinking is indeed a very literal action.
The pre-brain, or animal-brain, or Amygdala evolved in human evolution as a primtive information processor, only emitting a binary response - fear or pleasure. It is very stupid but very quick. It keeps one alive, uses very little energy, but is useless for day to day human activity. The pre-frontal cortex is a far more sophisticated organ, whose response to inputs includes no emotion, only logic, but takes more calories, and has a slower response time.
In a normal unenlightened brain, the amygdala responds faster than the PFC. By the time the PFC gets event data it is already meddled with by the Amygdala and has been characterized as positive or negative.
To attain being before thought we train in faster response and intelligent reponse.
When we do long hours of zazen, by choice-less-ly observing events, we strengthen the nervous system leading to the pre-frontal cortex, and weaken the nervous system leading to the amygdala. Exactly like strengthening a muscle with use, and atrophying another muscle with disuse. In time the PFC reacts faster than the Amygdala to everything leading to a very logical person who's not swayed by the emotional ups and downs of life.
However, this is a physical modification, and can change with age or injury.
The real permanent change is when we also train our logical faculties to learn to recognize and discard the emotional meddling of the amygdala if and when it arrives before the PFC. 
Thus even if an event is characterized as fearful or anger inducing by the Amygdala, by realizing no-self we can discard animalistic habit patterns, and utilizing the energy of mindfulness and wisdom we decide on the moment on its merits.
Eventually after practicing this until it becomes second nature, and by discarding identification and habit patterns we are finally before thought, and the turbid waters of the mind become still and clear.
CAVEAT: I am not a neural expert, this theory is solely based on personal inquiry, a little experience and a little hypothesis. YMMV.

-1: <p>His, Dogen's, Fukanzazengi, says</p>

<blockquote>
  <p>Think of not-thinking. How do you think of not-thinking? Be before
  thinking. These are the basics of zazen.</p>
</blockquote>

<p>I haven't, I think, been formally taught zazen. But how does this sound, as a paraphrase:</p>

<ul>
<li>think of thinking which is no longer thought</li>
</ul>

<p>Because, taken literally, I feel that it is a very good way of looking at our relationship to history, when we cannot do anything about it.</p>
 254: <p>To me the English phrase, "think of thinking which is no longer thought" implies that it <em>used</em> to be thought, that it was previously thought, but is no longer thought i.e. it is not thought any more. In other words it's something to do with <em>after</em> thought, not <em>before</em> thought.</p>

<p>The way I understand "before thought" is, for example, if I see a tree then what I'm seeing is light reflected off a tree: I'm seeing light after it's reflected (instead of seeing the tree itself). If I wanted to know the tree (i.e. reality) and not just know the reflected light (i.e. thoughts), then I ought to consider what's happening <em>before</em> the light is reflected.</p>
 8238: <p>I had a look at translations of Dogen's essay "Universally Recommended
Instructions for Zazen":</p>

<blockquote>
  <p>Think of not thinking. Not thinking-what kind of thinking is that?
  Nonthinking. This is the essential art of zazen.</p>
</blockquote>

<p><a href="https://web.stanford.edu/group/scbs/sztp3/translations/gongyo_seiten/translations/part_3/fukan_zazengi.html" rel="nofollow">https://web.stanford.edu/group/scbs/sztp3/translations/gongyo_seiten/translations/part_3/fukan_zazengi.html</a></p>

<p>I did further research on the text and came across the archaic Japanese original as well as the modern Japanese translation.</p>

<p>Dogen's Original Passage</p>

<blockquote>
  <p>箇（こ）の不思量底を思量せよ。不思量底、如何（いかん）が思量せん。非思量。これ乃（すなわ）ち坐禅の要術なり。</p>
</blockquote>

<p>Modern Japanese</p>

<blockquote>
  <p>不思量に止（とど）まり居る処のみを任運に、そのまま不思量底であるところ、本来の相としての非思量に在る。これが、まさに坐禅の要術である。</p>
</blockquote>

<p><a href="http://www.geocities.jp/sybrma/235.5hukanzazengi.yaku2.html" rel="nofollow">http://www.geocities.jp/sybrma/235.5hukanzazengi.yaku2.html</a></p>

<p>Now I am not a Japanese speaker, however the Chinese characters (Kanji) used in both passage are 不思量 and 非思量 which would roughly translates as 'not thinking' and 'non thinking'. Suggesting that 'be before thinking' is not a good translation.</p>

<p>Further research indicates the context that the phrase was used:</p>

<blockquote>
  <p>These words appear in a dialogue that Dogen makes the subject of SBGZ
  Zazenshin: A monk asked Yueh-shan, "What does one think of when
  sitting motionlessly in zanen?" Yueh-shan replied, "You think of
  not-thinking." "How do you think of not-thinking?" asked the monk.
  "Nonthinking," answered Yueh-shan.</p>
</blockquote>

<p><a href="http://www.sunypress.edu/pdf/60478.pdf" rel="nofollow">http://www.sunypress.edu/pdf/60478.pdf</a></p>

<p>This would suggest that the intent of his message was not about some kind of '<strong>prescience</strong>' (the fact of knowing something before it takes place; foreknowledge) as the word <em>be before thinking</em> or <em>before thought</em> would suggest, but the single pointed concentration that result in the falling away of thoughts.</p>

<p>This corresponds with the mental factors of the Jhana, which the the Pali root word for Chan/ Zen.</p>

<blockquote>
  <p>First Jhāna — the five hindrances have completely disappeared and
  intense unified bliss remains. Only the subtlest of mental movement
  remains, perceivable in its absence by those who have entered the
  second jhāna. The ability to form unwholesome intentions ceases. The
  remaining qualities are: "<strong>directed thought, evaluation</strong>, rapture,
  pleasure, unification of mind, contact, feeling, perception,
  intention, consciousness, desire, decision, persistence, mindfulness,
  equanimity &amp; attention"</p>
  
  <p>Second Jhāna — all mental movement utterly ceases. There is only
  bliss. The ability to form wholesome intentions ceases as well. The
  remaining qualities are: "internal assurance, rapture, pleasure,
  unification of mind, contact, feeling, perception, intention,
  consciousness, desire, decision, persistence, mindfulness, equanimity,
  &amp; attention"</p>
</blockquote>

<p>As noted, by the second Jhana all thoughts have ceased, only awareness of bliss and other Jhanic factors remains.</p>

<p>A poster here suggested that it could be to do with:</p>

<blockquote>
  <p>When one's perceptional faculties are acutely developed and on the
  cusp of awakening, logical perception will begin to occur before
  emotional perception.</p>
</blockquote>

<p>While this could possibly occur in meditation, it is not suggested in the actual text. Further more, given that the text was meant to be a <strong>universal recommendation</strong>, it would imply that the text was directed at general audiences, who do not have the necessary background in meditation. Who might be wondering what they are supposed to think during sitting meditation, the answer being not think of anything in particular. (A more systematic way is to direct your thoughts to an object of focus, for example your breathing).</p>
 715: <blockquote>
  <p>Think of not-thinking. How do you think of not-thinking? Be before thinking. These are the basics of zazen.</p>
</blockquote>

<p>When one's perceptional faculties are acutely developed and on the cusp of awakening, logical perception will begin to occur before emotional perception.</p>

<p>For example, if there is a loud bang, the first perception in the mind will be, just a loud bang, nothing to fear. The very next nano second, the emotional perception will arise, suggesting fear and panic. However this emotional message will have no relevance because the event has already been cognized logically.</p>

<p>In modern scientific terms, one could describe it as the speeding up of the logical brain over the pre-brain. </p>

<p>By intently examining every moment in zazen we cause the evolution of the response time of the brain's logical faculties. </p>

<p><strong>To be before thinking</strong> is indeed a very literal action.</p>

<p>The pre-brain, or animal-brain, or Amygdala evolved in human evolution as a primtive information processor, only emitting a binary response - <em>fear or pleasure</em>. It is very stupid but very quick. It keeps one alive, uses very little energy, but is useless for day to day human activity. The pre-frontal cortex is a far more sophisticated organ, whose response to inputs includes no emotion, only logic, but takes more calories, and has a slower response time.</p>

<p>In a normal unenlightened brain, the amygdala responds faster than the PFC. By the time the PFC gets event data it is already meddled with by the Amygdala and has been characterized as positive or negative.</p>

<p>To attain being before thought we train in faster response and intelligent reponse.</p>

<p>When we do long hours of zazen, by choice-less-ly observing events, we strengthen the nervous system leading to the pre-frontal cortex, and weaken the nervous system leading to the amygdala. Exactly like strengthening a muscle with use, and atrophying another muscle with disuse. In time the PFC reacts faster than the Amygdala to everything leading to a very logical person who's not swayed by the emotional ups and downs of life.</p>

<p>However, this is a physical modification, and can change with age or injury.</p>

<p>The real permanent change is when we also train our logical faculties to learn to recognize and discard the emotional meddling of the amygdala if and when it arrives before the PFC. </p>

<p>Thus even if an event is characterized as fearful or anger inducing by the Amygdala, by realizing no-self we can discard animalistic habit patterns, and utilizing the energy of mindfulness and wisdom we decide on the moment on its merits.</p>

<p>Eventually after practicing this until it becomes second nature, and by discarding identification and habit patterns we are finally before thought, and the turbid waters of the mind become still and clear.</p>

<p><strong><em>CAVEAT: I am not a neural expert, this theory is solely based on personal inquiry, a little experience and a little hypothesis. YMMV.</em></strong></p>
