# Inductive vs Deductive Reasoning Deductive reasoning does not acquire new information. Deductive reasoning is essentially tautological (circular) and non-informative. Its fundamental form is self-identity (A=A). Its advantage is a high level of certainty, or reliability. From given true premisses, a deductively valid argument guarantees the truth of the conclusion. It's also been figuratively said that the conclusion of a deductive argument is contained within its premisses. The very reason a deductive conclusion is guaranteed is precisely because it doesn't add any new information not already contained in the premises. But the question here is about inductive reasoning. You should note that there are a number of different types of induction. Mathematical induction, for example, is more like deduction except that it allows implicit iterations in the premisses (for example, if you can count 1, 2, then by induction you can skip 3, 4, 5, ... , etc. up to whatever number you want). But when most people think of induction, they are thinking about the empirical kind most often associated with science. In empirical induction, we start out with some observed phenomena, draw a deductive conclusion based on the observed phenomena, then by induction generalize from some cases to all. So if I observe a number of crows. I notice all the crows I've observed are black. I deductively conclude that all the crows I've observed are black. I then inductively generalize that all crows are black. That includes all the crows I haven't seen yet. The main advantage of inductive reasoning, and the reason that most of our reasoning is inductive, is that it works better in situations when our information is incomplete. For cognitive systems like ours, where our experience is very limited, inductive reasoning helps us draw sometimes life saving conclusion very quickly in the moment. In more formal arenas like science, inductive reasoning allows us to generalize laws of nature and the universe, even though our experience of it is an extremely small percentage, even if we include the entire collective experience of humanity over time. Where deductive reasoning is great for closed systems, inductive reasoning is great for open ones. The main disadvantages of inductive reasoning are (a) that it cannot guarantee its conclusions, (b) that it assumes the uniformity of nature throughout the universe, and (c) it relies on observation for information collection. It doesn't matter how many black crows you see, if you have't observed all crows, there is a chance that one you haven't seen is freakishly albino. This is the flip side of the main advantage of inductive reasoning. It's quick, but fallible. The assumption of the uniformity of nature has been a subject of debate through the history of philosophy. In order to generalize to a larger number of cases from smaller ones, we have to assume that nature works the same everywhere. While most of our observation has confirmed this assumption, there have been cases which have surprisingly not behaved as we assumed, particularly when we have generalized from the observational level to smaller ones. Once we developed the technology to see it, we found that microscopic reality looked a lot different than the inductive generalizations of it based on naturally observable phenomena. We found further weird results as technology allowed us to measure quantum phenomena. Explanatory principles based on uniformity and parsimony like Occam's Razor often fail given experimental data, especially it seems in biology and evolution. In science, experimental methods trump any notion of "best explanation". We also don't know how much of our perception of uniformity is based on our mechanisms of observation. Neurological evidence suggests that all of our conscious perceptions are pre-processed prior to our experience of observation. The brain may be trying to make sense of our perceptions prior to both our experience of them. Being that observation is so fundamental to inductive reasoning and science, it's remarkable how little we know about the process. Throughout the history of philosophy, traditional positions of rationalism and empiricism argued for either deduction or induction as fundamental to our reasoning. Today, just like we recognize a complex relationship between nature and nurture, and that it's not either or, most philosophers believe there is a necessary relationship between deductive and inductive reasoning. They always work together. Inductive reasoning requires deduction to define units, quantify them, and structure them within holistic paradigms. Deduction defines consistency and coherence within systems. But deduction is useless at giving us new information, making generalizations, and reasoning from limited experience. Observation, our primary source of new information, is neither deductive nor inductive. It's the processing of observation which is the combination of deductive and inductive processes. There are no direct raw observations which will function as true premisses in either deductive or inductive arguments.