The words previous and last can in many cases be used interchangeably. For example, I can refer to week before the current week as ‘last week’, but I can also say ‘in the previous week’. However, the word last also has a different meaning, namely that of final or ultimate. For example, if I were to change jobs, I could say ‘this is my last week’. It is important to keep that in mind when using the word last, because it can lead to confusion and ambiguity.
A good example, often encountered in scientific writing, is the following. When you refer to the previous chapter in a text or book, the expression
In the last chapter, …
is misleading because it can also be interpreted as referring to the final chapter of the book. Therefore, you should either write
In the previous chapter, …
or, even better,
In chapter x,
where x is the number of the chapter you are referring to.
Note that the same problem also exists in German, where the phrase
Im letzten Kapitel…
can either mean ‘in the previous chapter’ or ‘in the final chapter’. Both cases can be translated as ‘in the last chapter’, but the expression is ambiguous.