Like most stuff that gets introduced in lecture courses, it's mostly right, but more complicated.

Prior to the decision to drop the bomb, some members of the Japanese political leadership were working behind the scenes to try to negotiate a conditional surrender whose terms did (in many ways) closely resemble the unconditional terms of peace that was later accepted.

But both the American public and the American government were hostile to the idea of a conditional Japanese surrender, while the Japanese public and military were vehemently opposed to the idea of an unconditional surrender.

So much so, in fact, that even if U.S. forces had been willing to consider a conditional surrender and it had been a politically feasible option, U.S. military strategists believed that, even if Japan's political elite were acting in good faith during negotiations, they would never be able to convince the Japanese hardliners in the military to accept the negotiated outcome and actually surrender.

So your prof is right in that there were negotiations and discussions on the table to end the war without the bomb, largely on terms that wound up being acceptable after the bomb. But whether or not that alone made the bomb unnecessary depends on whether or not one believes that those negotiations would have been politically feasible to the people and powers that be on either side of the Pacific without the bomb.

If you're looking for sources on it, "Marshall, Truman, and the Decision to Drop the Bomb" by Gar Alperovitz, Robert L. Messer and Barton J. Bernstein talks about this a bit, as does (iirc) John Chappell's Before the Bomb.

Someone else has mentioned that the Japanese offered conditional surrender before the bombings - the most important condition being that the Emperor was spared. The U.S., meanwhile, were adamant about only accepting unconditional surrender.

"The Potsdam declaration in July, demand[ed] that Japan surrender unconditionally or face 'prompt and utter destruction.' MacArthur was appalled. He knew that the Japanese would never renounce their emperor, and that without him an orderly transition to peace would be impossible anyhow, because his people would never submit to Allied occupation unless he ordered it. Ironically, when the surrender did come, it was conditional, and the condition was a continuation of the imperial reign. Had the General's advice been followed, the resort to atomic weapons at Hiroshima and Nagasaki might have been unnecessary." (from a biography about McArthur - "American Caesar: Douglas MacArthur" by William Manchester).

Yes, there is some truth to the statement, but as others have already said it was more complicated, and hinged on the question of whether it was a conditional or an unconditional surrender. Despite the fact that the final surrender was unconditional, the terms imposed by the US were rather similar to the conditional surrender that the peace faction of the Japanese leadership had imagined.

Since it is topical, allow me to re-post a more in depth timeline of the surrender decision, cobbled together from some posts that I wrote a while back.

The best English language book on the Japanese side of the decision to surrender is Hasegawa's Racing the Enemy.

He uses the diaries of key decision makers among the big six, the recollections of people close to them, and the minutes of their meetings, to argue that the Japanese leadership was more concerned with the Soviets declaring war than they were with the atomic bombs. Illogical as it might sound, the Japanese leadership hoped to secure Soviet mediation to gain a more favorable surrender. The goal of this surrender was always preserving the kokutai (国体 - national polity / national essence - which can mean anything from the national structure to the mythic godhood of the Japanese Emperor and his unity with the people) Second, they didn't know about the longer term effects of atomic bombs, and Japanese cities being destroyed wasn't a new thing; 1 bomb instead of thousands, but the end result looked similar in terms of death toll and destruction.

Here is a breakdown of the Japanese activity in the final months. Page numbers are from Hasegawa.

Although the Soviet Union had renounced the Japanese neutrality pact in April of 1945, and the Japanese ambassador knew that looking for soviet mediation in the surrender was a lost cause, Japanese leaders largely ignored their ambassador's advice and insisted on pursuing the possibility of Soviet mediation.

June 18th, the [Supreme War Council](http://en.wikipedia.org/wiki/Supreme_War_Council_(Japan)) decided to pursue "option 3," seeking Soviet mediation, and Hirohito endorsed this action in a meeting with the Big 6(The Supreme War Council, minus the Emperor) on June 22nd (106).

June 30th, Sato, Ambassador to Moscow, telegrammed Togo, the Minister of Foreign Affairs, to tell him that the plan "...is nothing but pinning our hopes to the utterly impossible." Togo told him to do it anyway (123). Clearly, they were looking for a way to surrender months before they actually did, but they wanted it on their terms.

July 12, Not to be deterred, Hirohito decided that Japan should try harder if negotiations weren't going well, and appointed Prince Konoe special envoy to Moscow to secure Soviet mediation. The same day Togo Telegrammed Sato and asked him to relay their intentions to Molotov, but Sato was unable to contact him before he departed for Potsdam. Even though their ambassador had been rebuffed, the Japanese high command either did not relay the full message up to the Emperor, or they did not understand the gravity of the situation (123-124). Sato's messages of the impossibility of this task continued through the rest of July, and Togo responded by telling him that seeking Soviet mediation was the imperial will (144).

August 2nd, Togo continued to reject advice that Japan should accept the Potsdam Procalmation, and told Sato that the Emperor was concerned with the progress of the Moscow negotiations, adding that "the Premier and the leaders of the Army are now concentrating all their attention on this one point"(172).

Aug. 7, After the Hiroshima bomb, Togo telegramed Sato in Moscow regarding the Konoe mission, stating that the situation was getting desperate and that "We must know the Soviet's attitude immediately" (185). Obviously, they still hadn't given up hope on Soviet aid, and the possibility of Soviet mediation still seemed to be an alternative to surrendering unconditionally, even to the peace party. Molotov and Sato met on the 8th, and Molotov read him the declaration of war against Japan. Sato's telegram informing Tokyo never arrived.

Aug. 9th, Japanese Domei News intercepted a radio broadcast of the Russian declaration of war and Tokyo learned of it. Early in the morning Togo and top foreign ministry officials met and decided there was no choice but to accept the terms of the Potsdam Proclamation (197). Togo then secured the agreement of Navy Minister Yonai and Prince Takamatsu. Hirohito independently learned of the Soviet entry to the war and summoned Kido at 9:55 am, telling him "The Soviet Union declared war against us, and entered into a state of war as of today. Because of this it is necessary to study and decide on the termination of the war," according to Kido's Journal (198). Prime Minister Suzuki deferred to the Emperor's wishes and convened the War Council. Clearly, among the peace party, Soviet entry to the war swayed them to end the war not through Soviet mediation, but by accepting the Potsdam proclamation.

The war party was also shocked, as the diary of Army Deputy Chief Kawabe notes considerably more shock regarding the Soviets than it does regarding the bombing of Hiroshima. Nonetheless, Army Minister Amami was not ready to surrender.

At that meeting, the Big 6 learned of the Bombing of Nagasaki. According to the official history of the Imperial General Headquarters, "There is no record in other materials that treated the effect [of the Nagasaki Bomb] seriously." Similarly, neither Togo nor Toyoda mention it in their memoirs of the meeting (204). In the meeting the war party continued to defend the idea of defending the home islands to force favorable terms, but slowly fell to the peace faction. By the end, they had agreed to accept Potsdam, but still debated 1 condition vs 4.

After this, members of the peace faction arranged to meet with Kido urging him to urge the Emperor to support a single condition acceptance ("preservation of the imperial house" [peace] or "preservation of the Emperor's status in national laws" [war] depending on who phrased it). Kido then met with the Emperor, and afterward the Emperor agreed to call an imperial conference, at which he supported Togo's proposal, saying "My opinion is the same as what the Foreign minister said." All the members, including the war party signed the document in the early hours of August 10th (213). With that, the basic outline of surrendering was complete, although they changed the single condition changed to acceptance "on the understanding that the Allied Proclamation would not comprise any demand which would prejudice the prerogatives of His Majesty as a Sovereign Ruler," which became a sticking point in its potential to preserve the emperor's status as a god and commander of the military (212).

On the common debate about this "sacred decision," it is true that the Emperor was the deciding "vote," but the deliberations show his decision was shaped by those who were convinced to surrender by Soviet declaration of war to put his weight behind the plan they had laid out. His own statements also show the effect that Soviet Entry to the war was a major concern for him. Similarly, Soviet entry and lack of the possibility of negotiated peace weakened the war party's case.

In the intervening days between the 10th and the 15th things were fairly chaotic. The war faction got key members of the peace faction to agree that they would continue the war if the conditional acceptance were rejected. However, members of the Foreign Ministry believed they had to accept the Bynes note, informing them of the US rejection of the conditional acceptance, when they got it on the 12th. The army thought it was an unacceptable violation of their understanding of the kokutai, leading to a stalemate in the leadership. While leadership argued back and forth, members of the army General Staff plotted a coup on the 12th and 13th. Fearing Military action, Kido met with Hirohito on the morning of the 14th and convinced him to convene a combined conference of the Supreme War council and the Cabinet to impose his decision for unconditional acceptance of the Bynes note.

The decision to accept was made around 11:00 am on the 14th, starting debates about how to phrase the announcement to the people. Leadership feared that poor phrasing, especially regarding the kokutai, might result in army action against the decision. Meanwhile, the coup plotters planned to occupy the imperial palace and prevent the Emperor from informing the nation.

The Coup took place on the night of the 14th, with forged orders telling the imperial guards to protect the emperor. They occupied the palace and shut down all the communications in and out. Coup members who went to the Eastern Army for help found the army opposed and determined to put the coup down by force, which they apparently did successfully, as the coup was over by morning. When asked to support the coup a final time, Anami informed them that he was going to commit suicide, and did so.

The Emperor's speech was broadcast on Aug. 15th (planned for back on the 11th). It cited the bombs as a reason for surrender, but that is not sufficient evidence to determine the reasons for ending the war. First, that speech was carefully prepared and edited for public, military, and American consumption. Second, it is only one of several sources. Of the contemporary sources on why Japan surrendered, 3 (Konoe on Aug.9th, Suzuki's statements to his doctor on Aug. 13th, and Hirohito's Imperial Rescript to Soldiers and Officers on Aug. 17th) speak only of the Soviets, 2 (Hirohito's Imperial Rescript on the 15th and Suzuki's statements at the cabinet meeting of Aug. 13th) speak exclusively about the bombs, and 7 speak of both (297-298). Both played a role, but the deciding edge likely belonged to to Soviet entry.

In my Japanese history class in college the professor told us that while Japan did eventually approach the US through unofficial channels to discuss a possible surrender, they said that they wanted to "leave the prerogatives of His majesty intact", i.e. leave the emperor on the throne as their one condition. The US rejected this, saying they would only accept a completely unconditional surrender. The Japanese government's thinking on this was based on a very real fear that members of the public might decide to lynch government officials for getting Japan into the war, which was by then bitterly regretted by much of the population, with graffiti slogans such as "Stop the stupid Emperor's war" being seen. The military cabinet that had started the war were basically worried that they might suffer the same fate as Mussolini, and that close association with the emperor, combined with the preservation of the emperor system, was their best chance to escape such a fate. That's why they were continuing to order things like kamikaze attacks and ordering ordinary citizens to prepare to fight invading Allied forces with spears; they weren't so much "defending their country" as holding out for the best possible deal they could get for themselves with no real regard to the cost in human lives (as long as the human lives were not their own). Finally, after two atomic bombings, the Americans hinted that they would let the emperor remain on the throne, so the condition the Japanese government wanted was given to them in the end anyway.

I'm not sure but maybe he was referring to the "Mokusatsu" incident. Basically, the story says that the japanese government responded to the postdam declaration by using the word "mokusatsu" which has an ambiguous meaning and was mistakenly interpreted by the americans as "ignore with silent contempt" and the confusion may have led to the dropping of the first atomic bomb.

Source: https://www.nsa.gov/public_info/_files/tech_journals/mokusatsu.pdf

Edit for clarity.

The problem is what was known at the time about Japanese intentions. The allies had been "Island Hopping" on their way to Japan and had just managed to capture Okinawa in a long and very expensive campaign (it didn't even properly finish until August 45. It was fairly certain that the Allies would prevail against Japan but at what cost?

As with Ultra, the Allies pulled a lot of intelligence from intercepts in Asia, known as Magic. Wireless monitoring stations would capture the signals which would then be decrypted and used to inform the commanders.

The problem is that you need signals intercepts. Towards the end of the war, the Japanese, as with the Germans, fell back to using telephone lines as their need for long distance communications dropped. There was less high level material available to intercept.

There were estimates of the Japanese capabilities such as this report [PDF warning] that appeared in July 45. The Japanese retained a formidable ground defence capability.

There was still some information such as the diplomatic traffic (including the communication with Moscow) which could be intercepted, but less command traffic. The positions that the Japanese were attempting to take using the Soviets as intermediaries were apparent, see here [PDF Warning] but there were doubts as to what they meant. The worst case, option 3 flagged they were stalling for time.

If we go on, there were a further series of decrypts giving the arguments between Sato (ambassador to the USSR) and Togo (Japanese Foreign Minister). Togo rejected Sato’s advice that Japan accept unconditional surrender except for the “preservation of the Imperial House".

The allies could only conclude that the Japanese were not about to surrender unconditionally at that point. Factions may well have been but there was no way for the allies to understand who might prevail. This lead directly to the Potsdam Declaration where the Allies spelled out their demands. This was, of course, preparatory for the Bomb.

It is easy after the facts to say that the enemy was losing and we should "ease up". The same arguments have been made about Nazi Germany in respect of Dresden. In the case of Germany there had been the Ardennes campaign and in the case of Japan, there had been Okinawa. The enemy was failing but there could still be massive losses before the war could be concluded, so all methods must remain on the table. In the case of Japan, that meant the bomb.

Edit/Rewritten to include subsequent points.