“Men standing in opposite hemispheres will converse and deride each other and embrace each other, and understand each other's language.”
"Of Hemispheres, which are infinite; and which are divided by an infinite number of Lines, so that every Man always has one of these Lines between his Feet."
The Notebooks of Leonardo da Vinci (1883), XX Humorous Writings
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Leonardo Da Vinci 363
Italian Renaissance polymath 1452–1519Related quotes

In reference to the Alabama Council on Human Relations, an organization which was joined by King, whose church's meeting room was used to hold monthly meetings for the Montgomery chapter the council. Stride Toward Freedom: The Montgomery Story (1958)
1950s
Context: Although the Montgomery council never had a large membership, it played an important role. As the only truly interracial group in Montgomery, it served to keep the desperately needed channels of communication open between the races.
Men often hate each other because they fear each other; they fear each other because they don't know each other; they don't know each other because they can not communicate; they can not communicate because they are separated. In providing an avenue of communication, the council was fulfilling a necessary condition for better race relations in the South.

The Task of Social Hygiene, ch. 1 (1912)

Encyclical Fides et Ratio, 14 September 1998
Source: www.vatican.va http://www.vatican.va/holy_father/john_paul_ii/encyclicals/documents/hf_jp-ii_enc_14091998_fides-et-ratio_en.html

“We've never had problems. We love each other, understand each other, and get past anything.”
On her relationship with Jack White
Frampton, Scott (July 2007), "Jack & Meg White". Esquire. 148 (1):118-119
“In real conversations, we are always trying to outguess each other.”
Part One, Entropy, Randomness, Disorder, Uncertainty, p. 56
Fortune's Formula (2005)

Part IV, ch. 1
The Song of the Lark (1915)
Context: The great pines stand at a considerable distance from each other. Each tree grows alone, murmurs alone, thinks alone. They do not intrude upon each other. The Navajos are not much in the habit of giving or of asking help. Their language is not a communicative one, and they never attempt an interchange of personality in speech. Over their forests there is the same inexorable reserve. Each tree has its exalted power to bear.

“Men are at war with each other because each man is at war with himself.”
This is almost always attributed to US Ambassador Francis Meehan http://www.nndb.com/people/060/000121694/, though without citations, and only very rarely to Patton.
Misattributed