When was so much faith last put into diplomacy? From Iran to Cuba, conflicts long locked in bitter stalemates have recently received the “jaw jaw” treatment. These are welcome developments in an era where resorting to bombs has all too often been the stuff of global politics. But much of this leaves open the question of what exactly defines a successful negotiation. What does diplomacy actually entail? Which approaches are most likely to succeed, or at least appear credible?

This is why it’s worth giving more scrutiny to how the frontrunner for the leadership of Britain’s main opposition party has tried to explain his willingness to engage in dialogue with representatives of unsavoury groups from the Middle East and elsewhere.

Addressing criticism of his contacts with Hamas and Hezbollah, Jeremy Corbyn has explained that this was all about “determined dialogue and persistent diplomacy” in order to “forward peace processes”. Asked about his openness to the Kremlin’s take on Ukraine, he has not only resorted to the usual systematic anti-western discourse, but also indicated that showing a degree of understanding for Vladimir Putin is the right way to contribute to a solution.

Corbyn has reacted to some of the scorn by saying that dialogue does not amount to “endorsing a particular set of views”, and that “it is necessary to speak to people with whom there is disagreement – merely talking to people who already agree won’t bring about a settlement”.

Diplomacy obviously includes dialogue. But one major piece of the puzzle is missing in this line of reasoning. The art of negotiation and diplomacy, as thinkers as far back as Sun Tzu have well described, involves determining who holds the balance of power. Talking with dubious groups for the sake of it, simply as a gesture of goodwill, has little to do with diplomacy. Rather, it becomes a gesture of solidarity with your interlocutor.

Results are obtained if you use the tools of power – including coercion

For the sake of argument, let’s take Corbyn’s explanations at face value, and believe he disagrees with parts of what his controversial contacts say or do (although he hasn’t specified what exactly these disagreements are). His stance can then come across as very attractive to the many people who rightly want conflicts to stop. Talking to “bad guys” (again, assuming Corbyn thinks they are bad) is surely part of getting them to change their minds, or their policies. Indeed, you only make peace with enemies.

But, in practice, conflict resolution rarely consists just of words or warm gestures. In the real world of diplomacy, dialogue works only if the interests of both parties line up for a compromise, or if those who seek to reach a settlement are in a position to exert pressure on adversaries. Results are obtained if you use the tools of power, including coercion (which doesn’t necessarily mean military action).

To assume that the very fact of talking will mellow an adversary is historically naive. It is non-operational. When Obama said in 2009 that America would “extend a hand [to its enemies] if you are willing to unclench your fist”, this was seen as a welcome break from the Bush years, but it was important not to forget the last part of his sentence.

There is no example of conflict resolution without balance of power. The Bosnian war wasn’t ended just through diplomatic summitry. It ended when the balance of forces was modified on the ground, and irresistible pressure was exerted on Milosevic. The recent nuclear agreement with Iran wasn’t forged only on the basis of talking: it was made possible when Iran understood there was no other way to get economic relief from sanctions, which had severely increased in recent years.

When the US reached a diplomatic breakthrough with China in 1972, it wasn’t because Kissinger and Nixon had decided to be friendly to Mao. It was because a set of hardcore bilateral strategic interests had converged. Conflicts end through dialogue when opposing sides have exhausted all other options, when the benefits of compromise outweigh the cost of prolonging the dispute.

But when the readiness to talk is demonstrated without any leverage whatsoever, the outcome is just a PR stunt for the most dubious party involved. This is what happened when a group of French rightwing MPs met Bashar al-Assad earlier this year. The same occurred when Alexis Tsipras sat down to talk with Putin in Moscow. It’s no coincidence that Russia’s official media are currently giving Corbyn glowing coverage.

The point is not that talking with “bad guys” is wrong in itself. What matters are the circumstances, and how you lay out your strategy, and the means to achieve goals. George W Bush was mistaken not to engage with Iran back in 2003 when its regime seemed ready to unclench a fist after the invasion of Iraq. Europe must pursue difficult discussions with Putin, and results will be tied to the pressure exerted by sanctions. Diplomacy, as the Webster dictionary says, is either “the art and practice of conducting negotiations between nations”, or a “skill in handling affairs without arousing hostility”.

The diplomacy Corbyn has in mind is an ideological and complacent show from the sidelines, partly because he is not in power, but mostly because it is disconnected from how deals are reached in the real world.