There are many ways that historians can come to understand the cultural context. If we take, say, the late Elizabethan period and want to learn more about what people thought about other things then there's lots of ways that can be achieved.

Firstly we can look at the laws of the time. Obviously in most societies the traditional things like murder, robbery and assault are generally criminalised. However, certain more specific laws can tell us about what other behaviour was frowned upon. In England and Italy, the Sumptuary laws dictated who was allowed to wear what. This gives us a useful insight into fashion at the time. Additionally, the fact that things like these were banned in the first place indicates that they were occuring frequently enough to both be a problem and that they contradicted social norms to the extent that banning them was an acceptable solution. On a related note we can also look at trial records of the time. If the punishments given for the same crime vary based on the details, that can tell us about levels of acceptability in society. For example, if a murderer gets a reduced punishment because he committed a revenge killing, then that can tell us something about honour culture in this period.

Secondly, we can investigate literature and writing. We can take a big sample of literature and look at character archetypes. If the villains in English literature in a certain period are all French or corrupt Clergy then this can tell us about perceptions of France in this time, or how people felt towards the church. Similarly, we can look at what kind of behaviour is rewarded with a 'good' ending. In Ben Jonson's Volpone for example, the pious wife who refuses to sacrifice her chastity is rewarded whilst her husband and various other ne'er do wells are whipped, banished and imprisoned for their offences. The different sections of hell in Dante's Inferno give us a clue as to what sins and actions were seen as worse than others. Writings from different levels of society can often help as well. Whilst we are unfortunately limited to an elite view of society, as up until recently most lower class people were illiterate, letters, diaries and journals can provide us with social commentary on events. If lots of people write disapprovingly of a person's behaviour, we can infer that that kind of thing was frowned upon. Church writings, whilst probably tending to overexaggerate the scale of moral failings in society, can give us an idea of what perfect behaviour was seen as.

While it's impossible to get a completely clear view of what was seen as acceptable in a certain period and what was not, we can use the various sources available to us to create a decent idea. We may then apply that to the topic in question, allowing us to try and view these events through a contemporary lense. Naturally we are missing information about social norms and it's impossible to escape our modern worldview, but in the words of one of the Grandfathers of History Writing, Leopold van Ranke, we must attempt to capture wie es eigentlich gewesen, how it actually was.