Assam HS Class 11-12 Logic and Philosophy common mistakes
Assam HS Class 11-12 Logic and Philosophy · Understand the traps and how to avoid them.
When testing a categorical syllogism for validity, the candidate checks only whether the conclusion 'sounds right' or matches real-world facts, and never applies the rules of distribution, illicit major/minor, or the middle-term rules.
Everyday reasoning trains students to judge arguments by whether the conclusion is true, not by whether it follows. Assam HS textbooks introduce the five/six standard syllogistic rules, but under exam pressure candidates substitute content judgment for formal checking and skip the mechanical rule-by-rule pass.
What to do instead
Before writing anything, restate the syllogism in strict form (major premise, minor premise, conclusion), label S, P, M, then run a fixed checklist: (1) exactly three terms, (2) middle term distributed at least once, (3) no term distributed in the conclusion that was undistributed in the premise, (4) no two negative premises, (5) negative premise requires negative conclusion and vice versa, (6) particular conclusion cannot follow from two universal premises only if... verify with the standard rule set. Practise ten syllogisms a day using only the checklist, ignoring whether the conclusion is factually true.
The candidate marks a term as distributed in a particular affirmative (I) proposition, or fails to mark the predicate of a universal affirmative (A) as undistributed, producing wrong distribution tables and wrong immediate-inference answers.
Students memorise 'All S is P' as distributing both terms because the word 'All' feels totalising, and they carry that feeling into I propositions. The distribution rule is a formal convention (universal subject, negative predicate) that conflicts with ordinary language intuitions, so it is forgotten under time pressure.
What to do instead
Memorise the distribution table as a compact chant tied to quantity and quality: A distributes subject only; E distributes both; I distributes neither; O distributes predicate only. Write the four letters in a 2x2 grid with S and P columns and fill it from memory daily for a week. Then drill conversion, obversion, and contraposition only after the table is automatic, because every immediate-inference error traces back to a distribution error.
The candidate treats conversion of an A proposition ('All S is P' therefore 'All P is S') or conversion of an O proposition as valid, and confuses obversion with conversion when answering immediate-inference items.
In ordinary speech 'All dogs are animals' invites the reverse, and students do not distinguish the logical form from the conversational implicature. Conversion and obversion are taught close together, so the operations blur: conversion swaps terms without changing quality, obversion changes quality and negates the predicate.
What to do instead
Build a one-page operation chart: Conversion is valid for E and I only (A converts per accidens to I; O does not convert). Obversion is valid for all four (change quality, replace predicate with its complement). Contraposition is valid for A and O. For each item, first name the operation the question is asking for, then apply only that rule, and write the resulting proposition's letter before choosing an option.
When constructing or reading a truth table, the candidate fills the reference columns in the wrong order or with the wrong number of rows, so the final column is wrong even though the connectives were applied correctly.
The convention that the rightmost reference column alternates every row and each column to the left doubles the period is mechanical and easy to state but easy to misapply. Candidates also miscount rows for three or four variables (2^n) and run out of space or repeat combinations.
What to do instead
Always write n, compute 2^n, and draw exactly that many rows before entering any values. Fill reference columns right to left with periods 1, 2, 4, 8. Then evaluate innermost brackets outward, one connective per column, labelling each column with the sub-formula. Verify by checking that the main connective column is the last one written and that tautology/contradiction/contingency labels match (all T, all F, mixed).
The candidate confuses validity with truth, or soundness with validity, and answers 'the argument is invalid because the conclusion is false' or 'the argument is valid because the premises are true'.
The validity/truth distinction is the central conceptual leap of the course, and it is stated once in the textbook then assumed thereafter. Candidates who have not internalised the counterexample method fall back on evaluating the content of the premises and conclusion rather than the form.
What to do instead
Learn the definitions as separate one-line tests: an argument is valid iff there is no possible case in which all premises are true and the conclusion false; sound iff valid and all premises actually true. Practise by writing valid arguments with false premises and false conclusions (e.g., 'All fish fly; all flying things are birds; so all fish are birds') and invalid arguments with all-true premises and a true conclusion, to break the association. On every item, ask only 'can I imagine premises true and conclusion false?'
The candidate names fallacies by label without matching the label to the actual defect, e.g. calling an attack on the person 'appeal to authority', or labelling any circular argument 'begging the question' when the premise merely restates the conclusion in different words, and misidentifying undistributed middle as illicit process.
Fallacy names are learned as a vocabulary list rather than as diagnoses, and several fallacies (ad hominem, tu quoque, straw man; equivocation, amphiboly, composition) overlap in casual description. Under exam conditions the candidate pattern-matches a keyword in the passage to a familiar name.
What to do instead
For each fallacy, write the structural formula, not just the name: undistributed middle = M undistributed in both premises; illicit major = P distributed in conclusion but not in major premise; equivocation = same word, two senses across premises; ad hominem = premise attacks the arguer's character. When answering, first identify which term or word is doing the faulty work, then select the label that names that specific defect. Build a table of 'fallacy / structural signature / one original example' and revise from the signature column only.
The candidate describes inductive reasoning as a weaker form of deduction, or claims a strong inductive argument's conclusion follows necessarily, and cannot distinguish enumerative induction, analogy, and causal inference when a question asks which method is being used.
School teaching often presents deduction as the 'real' logic and induction as its informal cousin, so students absorb a hierarchy rather than a contrast of aims. Mill's methods and analogy are taught in a separate chapter and are not integrated with the probability language used for induction.
What to do instead
State the contrast in one sentence: deduction is truth-preserving (if premises true, conclusion must be true); induction is probability-raising (premises make conclusion more or less likely, never certain). Then classify by the inferential move: generalising from instances = enumerative induction; transferring a property from one case to a similar case = analogy; isolating a factor that co-varies with the effect = Mill's method of difference/agreement. Practise labelling ten short passages by the move, not by the subject matter.
The candidate answers Indian philosophy questions by listing schools and founders without distinguishing the orthodox (astika) from heterodox (nastika) systems, or attributes a doctrine such as anatta, maya, or syadvada to the wrong school.
The nine or so schools are introduced rapidly, and the memorable names (Nyaya, Vaisesika, Samkhya, Yoga, Mimamsa, Vedanta, Buddhism, Jainism, Carvaka) are easier to retain than the classification criterion, which is acceptance or rejection of the authority of the Vedas. Doctrines then get shuffled because the textbook presents them school by school rather than as a comparative grid.
What to do instead
Draw a two-branch tree: astika (Nyaya, Vaisesika, Samkhya, Yoga, Purva Mimamsa, Uttara Mimamsa/Vedanta) and nastika (Carvaka, Buddhism, Jainism). Under each school write its pramanas, its central metaphysical claim, and one signature doctrine (Nyaya: pramanas and syllogism; Samkhya: purusa and prakrti dualism; Advaita: maya and Brahman; Buddhism: anatta and pratityasamutpada; Jainism: anekantavada and syadvada; Carvaka: perception only, materialism). Revise from the grid, not from prose.
The candidate treats 'metaphysics' and 'epistemology' as interchangeable labels for 'philosophy', or answers an epistemology question (e.g., about the sources of knowledge) with a metaphysical answer (e.g., about the nature of reality), and cannot place rationalism, empiricism, and criticism correctly.
The branches are defined in the opening chapter and then never revisited, so the definitions fade. Rationalism and empiricism are also easy to invert because both are theories about knowledge and both are associated with famous names (Descartes, Hume, Kant) that candidates remember without the thesis attached.
What to do instead
Anchor each branch to its question: metaphysics asks what exists and what it is like (ontology, cosmology, theology); epistemology asks what knowledge is, how it is acquired, and how far it extends. Attach each school to a one-line thesis: rationalism - reason is the primary source of knowledge (innate ideas); empiricism - all knowledge derives from experience; criticism/Kant - knowledge requires both sense experience and the a priori forms of the understanding. On any item, first decide which question is being asked, then which school's thesis answers it.
The candidate treats 'term', 'proposition', and 'sentence' as synonyms, or classifies a proposition by its grammatical form rather than by its quantity and quality, so a rhetorical question or an exclamatory sentence is counted as a proposition.
The chapter on logic and language introduces the distinctions between sentence, proposition, and term quickly, and in ordinary usage the words overlap. Classification of categorical propositions depends on identifying quantity (universal/particular/singular) and quality (affirmative/negative), which requires paraphrase into standard form, a step candidates skip.
What to do instead
Fix the definitions: a term is a word or phrase that can stand as subject or predicate; a proposition is what a declarative sentence asserts and is capable of truth or falsity; a sentence is a grammatical unit that may express a question, command, or exclamation and thus no proposition. Then always paraphrase into standard categorical form ('All S are P', 'No S are P', 'Some S are P', 'Some S are not P') before assigning A, E, I, or O, and note that singular propositions are treated as universal for syllogistic purposes.