The labels inductive and deductive may be applied to several things, including methods of reasoning and methods of studying. A deductive approach moves from the rule to the example, and an inductive approach moves from the example to the rule.
I will first discuss deductive and inductive methods of reasoning (I have discussed these in greater detail elsewhere), then I will discuss deductive and inductive methods for studying.
The deductive method reasons from certain premises to a necessary conclusion. It is often described as reasoning from the general to the specific.
Premise: All men are mortal.
Premise: Socrates is a man.
Conclusion: Socrates is mortal.
If the premises are true, and the form is correct or valid, then the conclusion is necessarily true. However, if the form is invalid, then the conclusion is not necessarily true.
Some men are mortal.
Socrates is a man.
Therefore Socrates is mortal.
Though we may know that Socrates is mortal, nevertheless that does not logically flow from the premises of this argument. If we only know that some men are mortal, then Socrates might be among some men who are not mortal. The form of the argument is not valid.
The inductive method reasons in the opposite direction of the deductive method. It begins with specific observations and reasons to a generalization about the observations. It is often described as reasoning from the particulars to the general.
I have examined ten thousand dogs.
Every dog I have examined has fleas.
Therefore, all dogs have fleas.
The conclusion (really, a generalization) may possibly be true there is no observation which contradicts the conclusion but it is not necessarily true there are still more observations which could be made.
If, indeed, I had examined all dogs (which, of course, nobody could possibly do), and all dogs examined had fleas, then I could conclude that all dogs do indeed have fleas. Based on my sample of dogs, it appears that all dogs have fleas. But the first dog I found which did not have fleas would contradict and therefore disprove my conclusion. So all that I actually know is that some dogs have fleas.
The deductive method of reasoning moves toward necessary conclusions derived from correct connections between premises premises which are all either given or assumed to be true.
The inductive method of reasoning moves toward possible conclusions derived from hypothetical connections between premises (observations) which are selected from among all possible true premises (observations).
Ideally, the deductive method of reasoning is objective in its conclusions (the conclusions are necessarily true), but subjective in its premises (the premises are assumed to be true).
Ideally, the inductive method of reasoning is subjective in its conclusions (the conclusions are not necessarily true), but objective in its premises (the premises are observed to be true).
To begin with, if we believe that all of the propositions of the Bible are absolutely true, then we must believe that if we arrive at deductive conclusions by connecting the propositions of the Bible in a formally valid way, then these deductive conclusions are absolutely true. Therefore, deduction from the Bible results in absolute certainty. Many doctrines are arrived at deductively from the Bible, and it is these deduced doctrines which are the most widely accepted doctrines among Christians simply because they are proven (at least to the satisfaction of many if not most persons) and cannot be refuted without rejecting the full authority of the Bible.
Secondly, if we selected certain propositions from the Bible and weaved them into a pattern which is not based on necessary connections (that is, they are formally valid), but rather the pattern is based on our conjectured connections (that is, what looks best to us), then we can place no certain confidence in our conjectured patterns. In other words, induction from the Bible does not result in any absolute certainty. Many theological or dogmatic systems for interpreting the Bible are arrived at inductively, and it is these induced systems which are the most divisive among Christians, creating various schools of theology and denominations simply because different persons prefer different conjectures and are not willing to stay within the boundaries of what is provable.
Of course there are differences of opinion as to what actually is provable from the Bible, but this is not due to any defect in deductive reasoning. Rather, this may be compared to the proverb that computers actually don't make mistakes, it is the programmers or the operators who make the mistakes. Because the Bible does not (for the most part) come in the form of nicely formulated and completely unambiguous propositions, the element of interpretation is introduced, and this is where we humans often fail. In addition, we often fall into various fallacies deceptive errors in reasoning which lead us in the wrong direction.
Some believe that we can prove the Bible is true with logic. This is an unbiblical rationalism which places the authority of reason above the Bible. In order to prove the Bible, we would need propositions of higher authority than the Bible which is impossible by definition. However, if given enough time, we could conceivably prove all non-Biblical systems of thought to be self-contradictory and therefore false, which would leave the Bible standing as the only example of something which has not yet been proved self-contradictory. Nevertheless, we cannot prove the negative. So the truth of the Bible must ultimately be revealed to the individual. The Bible is self-authenticating, but only for those who have been brought within the circle of faith.
Some believe that we cannot prove anything from the Bible. This is an unbiblical irrationalism which denies that reason can be applied to the Bible. Instead, we must add experience and guesswork and take some leaps into uncertainty by faith.
We believe that the correct role of reasoning is as our servant to help us to understand the Bible. The place of logic is in submission as a servant to the Word of God.
A method is a regular way or manner of proceeding with or of accomplishing something. We must make a distinction between a method of reasoning to conclusions, and a method for studying a book or a subject.
For example, consider the inductive and deductive methods for studying a language:
Deductive language learning involves memorizing the various parts and categories of a foreign language and learning how to fit it all together and to us it. In other words, it begins with certain accepted principles of the language, then deduces the language as a whole from the correct combination of the parts and principles.
Inductive language learning involves reading passages in a foreign language, then picking it apart and learning what the parts mean. In other words, it begins with the language as a whole properly connected in all of its parts and principles, then figures out certain parts and principles of the language.
As you can see, we aren't actually talking about a method of reasoning so much as we are talking about a method of approaching a subject.
In the deductive method of study, we take for granted the work which others before us have done in identifying and categorizing various parts and their relationships of language (or any other subject), and we use this to develop our understanding of the whole system and to generate true examples of the language (or any other subject).
In the inductive method of study, what was taken for granted in the deductive method is here our primary work. We move from the given true examples of the language (or any other subject) and we break it down into its parts and relationships and thereby develop our understanding of the whole system
In actual practice, though any one method of study may be characteristically deductive or inductive, nevertheless nothing is purely deductive, and nothing is purely inductive, but they are actually used to serve each other.
Used correctly, both inductive and deductive Bible study methods can be helpful in using the Bible to arrive at or to test ones beliefs. Each has its special uses and abuses. I will describe each method below on the basic level, then on the advanced level, pointing out some uses and abuses.
Deductive Bible study on the basic level is simply instruction in Biblical doctrine. A better name for this might be synthetic Bible study [Greek: suntithemai to put together] because it puts together the separate elements of the Bible to form a coherent whole which is more highly developed than the parts. In a deductive study we might examine a previously selected series of Biblical texts in order to gather up Biblical propositions which, when properly arranged, prove such doctrines as the deity of Christ, or the personality of the Holy Spirit, or salvation by the blood atonement of Christ. The Apostles reasoned with them from the Scriptures, explaining and demonstrating that the Christ had to suffer and rise again from the dead.(Acts 17:2-3) So a deductive study is topical in nature, and someone must first do the work of finding the texts and arranging them to prove the doctrine, then we examine his work, benefit from it, and perhaps even improve upon it. The deductive study saves us much of the work of assembling these texts and building these doctrines on our own. In this way those young in the faith can be quickly edified [built up] line upon line in basic, essential, and important doctrines of the faith.
One common way of doing a deductive study is for the student to examine a selected series of Bible texts, then to answer specific questions about each text questions which will draw out and pull together the logical inferences so that the student can think for himself step-by-step through the logic of the doctrine.
Of course, in deductive Bible study the student must place a reasonable amount of trust in his teacher to guide him through the doctrines. Nevertheless, there are some things hard to understand, which untaught and unstable persons twist to their own destruction, as they do also the rest of the Scriptures.(2 Peter 3:16) The danger of the deductive study is that, regardless of the teachers intentions, we may be mislead. So the student must also examine for himself the Bible texts in their contexts to see if they say what the teacher thinks they say, and He must test the logical connections to make sure they prove what the teacher thinks they prove. The Bereans were more fair-minded than those in Thessalonica, in that they received the word [of the Apostles doctrine] with all readiness, and searched the Scriptures daily to find out whether these things were so. Therefore many of them believed.(Acts 17:11-12) Both the teacher and the student are accountable to the Lord, as well as to each other in the Lord.
Religious cults use a deductive method of Bible study in order to keep followers at a more childish level of understanding and thereby dependent upon them for instruction. The ultimate goal of a faithful Bible teacher is to bring his students up to his level of skill in understanding so that they may eventually instruct and correct him. Pastors and teachers, for the equipping of the saints for the work of ministry, for the edifying of the body of Christ, till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ; that we should no longer be children, tossed to and fro and carried about with every wind of doctrine, by the trickery of men, in the cunning craftiness of deceitful plotting, but, speaking the truth in love, may grow up in all things into Him who is the head Christ from whom the whole body, joined and knit together by what every joint supplies, according to the effective working by which every part does its share, causes growth of the body for the edifying of itself in love.(Ephesians 4:11-16) We have much to say, and hard to explain, since you have become dull of hearing. For though by this time you ought to be teachers, you need someone to teach you again the first principles of the oracles of God; and you have come to need milk and not solid food. For everyone who partakes only of milk is unskilled in the word of righteousness, for he is a child. But solid food belongs to those who are of full age, that is, those who by reason of use have their senses exercised to discern both good and evil. Therefore, leaving the discussion of the elementary principles of Christ, let us go on to maturity.(Hebrews 5:116:1)
As long as the doctrine is actually demonstrated by correctly handling genuine and valid proof texts, then this method of study can be very edifying, useful, and fruitful. [A valid proof text is a proposition found in the Bible which can be clearly shown to mean only one thing.]
However, deductive (or synthetic or doctrinal) Bible study should be clearly distinguished from dogmatic Bible study, which is instruction using selected texts as evidence to support a particular model or system of interpretation. [A supporting evidence text is a statement found in the Bible the meaning of which is open to interpretation it might be honestly interpreted to mean something other than what fits a particular model or system. Compare biological and archeological facts which are made to fit both evolutionary and creation models.] Dogmatic Bible study may appear on the surface to be the same as deductive Bible study, but the critical difference is that deductive study carefully demonstrates what the Bible teaches, while dogmatic study shows how a particular teaching might be fitted into the Bible whether it belongs there or not. In the deductive study we are led to trust the teachings of the Bible, while in the dogmatic study we are led to trust a system of teachings or dogma. A particularly dangerous form of dogmatic Bible study is when a special set of interpretations of certain key words, phrases, and passages are imposed upon Bible texts sometimes using a specially invented vocabulary in order to make the texts to fit into an otherwise unproven system for interpretating the Bible. Much time can be spent attempting to disentangle and unravel tightly bound systems of traditions or dogma or opinions which have been imposed upon the Bible.
At the more advanced levels of deductive study, instead of relying on a teacher to instruct the student, the student himself is involved directly in building and applying Biblical doctrine. A better name for this might be research Bible study. After obtaining a good knowledge of Scripture and a familiarity with how to prove doctrines, the student may take up the work of thoroughly searching the Scriptures and making His own necessary inferences from the propositions of Scripture. He may be motivated by special questions or controversies, or by issues and situations he has encountered which require a decision. His goal is to discover, if possible, the Biblical doctrine or principle which applies or offers guidance. The more tools the student has, the more effective he will be in accomplishing his goal. Topical lists of Scripture, concordances, cross-references, chain-references, and other reference books are valuable here. Used properly, an acquaintance with the original languages and access to language tools can insure a higher degree of accuracy in research.
The danger in research Bible study is that we may weave a web of interpretations which appears to support our own desires or expectations. In other words, we may deceive ourselves by impressing our own thinking into the Bible instead of allowing the Bible to impress its thinking upon us. For this we must always be on guard.
Theology textbooks often contain much excellent deductive instruction, but the dogma of the author is always intertwined with his deductive instruction, so it is often best to read the criticisms and dissenting opinions of other authors in order to help to discern what is Bible doctrine from what is the authors denominational opinions or personal conjectures. (Some insist there is a difference between systematics which is supposed to be purely Biblical doctrine and dogmatics which is supposed to be the study of a creedal system of a denomination or a theological model developed by a religious movement. From a practical point of view, it is often difficult to distinguish any real difference.)
Inductive Bible study on the basic level is simply careful instruction in the meaning of the Biblical text. A better name for this might be analytic Bible study [Greek: analuein to undo, to loosen back (to the elements)] because it breaks down Bible texts into parts or principles in order to examine its meaning and relationship to other texts.
In an inductive study we might examine a particular passage or book of the Bible, attempting to understand what the text means within its context. The purpose is not to build doctrine although a little of that will probably happen but the purpose is to build basic knowledge and understanding of the Bible. From childhood you have known the Holy Scriptures, which are able to make you wise for salvation through faith which is in Christ Jesus. All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work.(2 Timothy 3:15 - 4:1) So an inductive study is textual in nature, requiring much time in carefully examining larger continuous passages of Biblical texts in order to know what they mean and how they may apply to our lives.
One common way of doing an inductive study is to choose a large passage to examine word by word, phrase by phrase, paragraph by paragraph with a series of such questions as Who? What? Where? When? Why? How? What kind of? How many?which help to draw out some of the meaning of the text
1) We begin with the observation level, determining what the text says.
2) We next move to the interpretation level, determining what the text means by what it says.
3) Finally we move to the application level, determining how to apply what the text means to issues of modern life.
This follows the progression of the Biblical trivium:
1) Knowledge of the facts = observation of what the text says.
2) Understanding of the relationships = interpretation of what the text means.
3) Wisdom in applying the understanding = application of the interpretation to life
One weakness of this method is that someone may become so focused on the details of the text and the immediate application that he may not see the larger picture and therefore he may overlook or even disparage doctrine. In our age, the focus on personal insight and personal application may have engendered an aversion to doctrine. People do have trouble seeing, or even wanting to see the forest for the trees. This imbalance may be corrected with deductive doctrinal studies, and with thematic outlining of larger portions of Scripture.
If inductive study were our only method of study, then we would be less built up or edified in the doctrines of the faith. Inductive study is a good preparation for advanced deductive study, but it is no substitute for it. One who keeps away from deductive study and only does inductive study will withhold from himself the sure and certain knowledge of many edifying doctrines of Scripture. He who does not advance to the solid food of doctrine will remain as a child on milk. Children are more easily misled and are the least prepared to sense danger or to protect themselves or defend others in danger. And I, brethren, could not speak to you as to spiritual people but as to carnal, as to babes in Christ. I fed you with milk and not with solid food; for until now you were not able to receive it, and even now you are still not able; for you are still carnal.(1 Corinthians 3:1-3)
At the more advanced levels of inductive study, the student gathers information in order to look for patterns or trends in the Bible. A better name for this might be theoretical Bible study. A theory is a system of assumptions, speculations, or conjectures weaved together to explain certain observed phenomena, but which lacks verification either with direct connecting evidence or with proof by necessary inference. If any such inductive theories are then brought into subjection to deductive proof from the Bible, then they can be very useful. But if they are pressed on others without proof, they become false and useless knowledge which generates strife and divisions among brethren. Charge some that they teach no other doctrine, nor give heed to fables and endless genealogies, which cause disputes rather than godly edification which is in faith.(1 Timothy 1:3-4) If anyone teaches otherwise and does not consent to wholesome words, even the words of our Lord Jesus Christ, and to the doctrine which accords with godliness, he is proud, knowing nothing, but is obsessed with disputes and arguments over words, from which come envy, strife, reviling, evil suspicions, useless wranglings of men of corrupt minds and destitute of the truth, who suppose that godliness is a means of gain. From such withdraw yourself.(1 Timothy 6:3-5) Guard what was committed to your trust, avoiding the profane and idle babblings and contradictions of what is falsely called knowledge by professing it some have strayed concerning the faith.(Timothy 6:20-21) Hymenaeus and Philetus are of this sort, who have strayed concerning the truth, saying [speculating] that the resurrection is already past; and they overthrow the faith of some.(2 Timothy 2:17-18) For the time will come when they will not endure sound doctrine, but according to their own desires, because they have itching ears, they will heap up for themselves teachers; and they will turn their ears away from the truth, and be turned aside to fables.(2 Timothy 4:3-4)
Theorizing is not in itself necessarily bad in fact, it can be very useful but when it takes on a life and authority of its own apart from Bible, it becomes an enemy of the true doctrine and faith of the Bible. We might compare this somewhat to the theory of evolution. Micro-evolution is the shifting of gene pools in a population in order to adapt a species to circumstances. This was originally a scientific induction, but it may now be considered verified as observable fact. Macro-evolution, on the other hand, is the changing of genetic materials in order to create altogether new species. This is a theoretical model which has never been observed and which appears to contradict observable fact (not to mention Scripture). Micro-evolution has proven to be a useful theory because it has since been proven to everyone's satisfaction. Macro-evolution is a useless speculation which can never be proven true, and which many consider to have been falsified in several ways. Its only useful purpose has been to eliminate that line of reasoning.
Deductive or synthetic Bible study gathers propositions from Scripture and arranges them as premises in formal arguments which reason toward necessary doctrinal conclusions which may not otherwise have been stated in the Bible. In this way, it builds Biblical doctrine. On the basic level, the gathering and arranging of Scripture to prove doctrines has already been done for the student. On the advanced level, the student researches these on his own.
Inductive or analytic Bible study examines in detail large passages of Scripture in order to understand those passages in context. In this way, it builds a general understanding of the Bible. On the basic level, the student researches on his own. On the advanced level, the student surveys all or large portions of Scripture looking for patterns, and theorizes about the meaning of what he observes. He then goes back and attempts to prove his theory deductively.
So inductive and deductive study go hand in hand. Inductive study supplies the analytical Bible knowledge and understanding necessary to deductively build Bible doctrine, and deductive study researches and builds doctrine which informs inductive study concerning the wider doctrinal context of Scripture which then enables inductive study thereby to draw out even more meaning from the text.
The weakness of inductive study is its limitations in building doctrine, and the weakness of deductive study is its susceptibility to being infected with dogma.
The abuse of inductive study comes when theory is turned into dogma, and the abuse of deductive study comes when dogma is mixed with doctrine.