From its beginnings in oral storytelling, history was a partly literary exercise (and thus a part of the humanistic tradition) until it became professionalized in the nineteenth century.
From at least that time, history has also been counted as a social science because modern historians use objective data as evidence to support larger claims, and employ methods that are loosely based on the logic behind the scientific method. Some of our evidence is empirical (gathered through experiment or observation, as in the natural and social sciences), and some is interpreted through the “close reading” of texts (as is the evidence in other humanities fields, like literature and philosophy). In fact, as the study of everything that has happened in the past, in a way history can be said to encompass all other disciplines, with all their diverse methodologies.
Historians also rely on an exceptionally broad range of types of evidence: we use documents of every kind (public and private, statistical, official, informal, etc) as well as literature, but also fine arts, everyday objects, architecture, landscape, data on demographics, climate, health, etc, and just about anything else.
What holds together this very broad field is simply that we all study the past. That is, a historian of science may need to master many principles and methods of scientific inquiry, but her goal is to understand the development of science over time; contrast this to the scientist who may share some principles and methods with the historian of science, but whose goal is to further new scientific knowledge, rather than to understand how it developed up to the present.
More specifically, historians can be distinguished from scholars in other fields by the kinds of questions we ask. The questions historians ask can usually be reduced to some combination of the following:
(a) change and continuity over time
(what changes & when, what stays the same while other things are changing)
(b) cause and effect
(which factors affect which outcomes, how and why)
Dates, events, and famous names are elements we seek to master only so that we can more accurately explain the bigger questions of continuity, change, cause and effect.
Understanding the past helps us to know ourselves better (since we are in many ways the products of our pasts), and also to understand in a broad sense how societies behave, and how the constraints of particular societies affect their behavior.
This understanding – though always and inevitably imperfect – is both worthwhile in its own right and can also help us to better understand our choices in the present.
Although historical methods are often grounded in theoretical models and strategies (as in all academic disciplines), historians place unusual emphasis on distinguishing between specific contexts (time, place, social/intellectual/political/cultural climate, etc), as opposed to other disciplines which often aim to formulate models that apply accurately to many contexts.
On other words, we’re not lumpers, we’re splitters.
For example, when we as a society wonder about the causes of war, a political scientist may seek to distill the common factors causing many past wars so as to ultimately formulate a working general theory that will (one hopes) accurately predict the causes of future wars.
The historian, on the other hand, is more likely to delve into the unique factors of each particular context in order to understand what caused that war (but not others).
The historian’s ultimate goal, in this example, is to discern how particular contexts affect particular causes – i.e., identifying unique factors and tracking how they affect other factors), rather than directly predicting future events or reducing particular phenomena to general principle.
Note that both approaches are valuable and informative, and – interestingly – they each can serve as a check on the excesses of the other.