Lysimachus, son of Aristides, and Melesias, son of Thucydides (not the historian Thucydides), request advice from Laches and Nicias on whether or not they should have their sons (who are named after their famous grandfathers) trained to fight in armor. After each gives their opinion, Nicias for and Laches against, they seek Socrates for counsel.
Socrates questions what the initial purpose of the training is meant to instill in the children. Once they determine that the purpose is to instill virtue, and more specifically courage, Socrates discusses with Laches and Nicias what exactly courage is. The bulk of the dialogue is then the three men (Laches, Nicias and Socrates) debating various definitions of courage.
Nicias argues in favor of an education in fighting in armour for young men. He mentions that it promotes physical fitness, prepares a man for military duties, gives an advantage over untrained opponents, helps one understand military strategy, makes one braver, and gives one a martial appearance.
Laches argues against the need for fighting in armour by claiming that the Spartans do not practice it; the instructors that Laches has seen are not brave soldiers and so have not benefitted from this knowledge; and it causes cowards to take foolish and damaging military risks.
Melesias and Lysimachus ask Socrates to decide which side is correct. Socrates begins by trying to clarify what the actual topic is. He determines that the issue is the care of young men's character and asks if there are qualified teachers for this. Socrates confesses not to be skilled in this and assumes that Laches and Nicias are either versed in character building or else know of experts in that field. Socrates proposes to question them about this to see if they have qualified expertise.
Nicias warns about Socrates' philosophical methods of getting the interlocutor to examine their own conscience. Laches states that he likes to hear discussions that are "musical", when a person's discourse is in tune with their actions. Paraphrasing Solon, Laches agrees to participate in Socrates' inquiry because he likes to learn from good men.
Socrates uses a medical analogy to help define goodness: If eyes can be improved by adding sight to them, then a boy's character can be improved by adding goodness to it. As knowledge of what sight is is necessary before it can be considered as an improvement, so too it is necessary to have knowledge of what good is before it is used to improve a character. Rather than try to define what the whole of goodness is, Socrates thinks it would be easier to define an aspect of goodness that is relevant to the question: bravery.
Laches advances that to be brave is to be a soldier who can hold his position in combat without running away. Socrates explains that his definition is very specific to military infantry and what he was really looking for is a notion of bravery that pertains to all military situations and extends to all situations in life.
Laches offers an opinion that courage is "a certain perseverance of the soul". However, Socrates challenges this idea by arguing that there are many instances in battle when the prudent thing to do is to withdraw or flee. Since courage is a virtue, Socrates argues, it cannot contradict prudence, and therefore the idea that courage always demands perseverance must be false. Laches is forced to admit this contradiction.
Socrates expresses his perplexity in trying to account for bravery. Laches wishes to pursue the conversation, saying that he has a sense of what bravery is, but is not able to express it properly. Socrates states that like a good huntsman pursuing a trail, they must persevere in the search for their quarry. They invite Nicias to give his definition of bravery.
Nicias then offers another definition. He suggests that courage is "knowledge of what is to be feared and hoped for both in war and in all other matters".
Since bravery is the knowledge of what is fearful and encouraging, Socrates asks if a pig could be brave. Nicias denies that animals can be brave as he believes that a certain amount of wisdom is necessary for bravery and that very few people can be considered brave. Socrates playfully suggest that Nicias is being influenced by a sophist named Damon and offers to respond to Nicias' assertion.
Nicias agrees that something 'fearful' is the expectation of a future evil and something 'hopeful' is the expectation of a future good. Socrates then argues that full knowledge of any subject involves an understanding not only of future matters, but also of past and present. Thus if courage is the knowledge of future evils and goods, it must also necessarily be the knowledge of
And so, in the end, Socrates finds both his companions' theories to be unsatisfactory, and the dialogue ends in aporia, an English term derived from the ancient Greek meaning "philosophical confusion".
There are many different interpretations as to why the dialogue ends in aporia. Certain commentators, such as Iain Lane, view the Socratic method of elenchus as an end in itself; that debate is the central premise and function of the dialogue. Others, such as Gregory Vlastos, see the dialogue ending because of the specific deficiencies of the characters' definitions.
Some of the characters in this dialogue were famous military statesman who died in battle. Nicias was a prominent Athenian politician and general who died during the Sicilian expedition. Laches was also a general and died at the Battle of Mantinea in the Peloponnesian war. It is not surprising that Socrates would question them on the importance of military training and the definition of courage. This gives the dialogue's place in ancient Greek history a clearer importance.