ACT Vocabulary Guide

“"The scientist published her results" is an independent clause; it stands alone as a complete sentence.”

“"Because the experiment failed" is a dependent clause — it cannot stand alone. Attach it to an independent clause: "Because the experiment failed, the team revised their hypothesis."”

“"The data was collected, it was then analyzed" is a comma splice. Fix it with a semicolon: "The data was collected; it was then analyzed."”

“"She ran the trial twice the results were inconsistent" is a run-on. Correct: "She ran the trial twice, but the results were inconsistent."”

“"Although the study was well-designed." is a fragment. It needs an independent clause to complete it.”

“In "She wore a red hat," "red" is a modifier describing "hat." Misplaced modifiers create confusion about what is being described.”

“"Exhausted from the exam, the couch seemed inviting" is a dangling modifier — the couch wasn't exhausted. Correct: "Exhausted from the exam, she found the couch inviting."”

“In "The student submitted her paper," "student" is the antecedent of "her." Pronoun-antecedent agreement is heavily tested on the ACT.”

“"She enjoys hiking, swimming, and to run" violates parallel structure. Correct: "She enjoys hiking, swimming, and running." All items must be the same grammatical form.”

“A comma + coordinating conjunction joins two independent clauses correctly: "She studied all night, but she still felt unprepared."”

“Common subordinating conjunctions: because, although, since, while, when, if, unless, until, after, before. "Although the data was incomplete, the researchers proceeded."”

“"My sister, a biochemist, works at the university." The phrase "a biochemist" is a nonessential appositive and is set off by commas.”

“ACT "Production of Writing" questions are rhetorical — they ask whether a sentence adds relevant detail, whether a paragraph is in the right order, or whether a transition is logically appropriate.”

“"The ancient artifact was very old" is redundant — "ancient" already means old. On the ACT, the shorter, non-repetitive choice is almost always correct.”

“ACT Knowledge of Language questions ask you to select words with the right diction — precise, appropriate, and consistent with the passage's tone and register.”

“The experiment was carefully designed; however, the results were inconsistent with the hypothesis.”

“The initial funding was insufficient; nevertheless, the research team completed the project on time.”

“The new policy reduced costs; furthermore, it improved employee satisfaction across all departments.”

“The medication proved effective; moreover, it produced no significant side effects in the trial participants.”

“The city's water filtration system failed during the flood; consequently, residents were advised to boil drinking water.”

“Carbon dioxide absorbs infrared radiation; therefore, increasing atmospheric CO₂ levels intensify the greenhouse effect.”

“The survey sample was too small to represent the full population; thus, the findings should be interpreted cautiously.”

“Although the initial results were promising, the long-term outcomes did not support the researchers' original hypothesis.”

“Classical conditioning relies on involuntary responses, whereas operant conditioning shapes voluntary behavior through rewards and punishments.”

“High population density drives up housing costs in urban centers; conversely, rural areas often offer far more affordable living.”

“Urban infrastructure provides economic opportunity; on the other hand, it often displaces lower-income communities during development.”

“The northern region experienced record rainfall; in contrast, the southern provinces suffered a severe drought during the same period.”

“Many animals have developed remarkable survival adaptations; for example, the arctic fox changes its coat color seasonally to camouflage with its environment.”

“Several regions face severe water scarcity; in particular, the Colorado River Basin has seen reservoir levels drop to historic lows.”

“Admittedly, the proposed solution is expensive; however, the long-term costs of inaction far exceed the initial investment required.”

“In an experiment testing how temperature affects enzyme activity, temperature is the independent variable — the researcher sets it at different values deliberately.”

“If temperature is the independent variable in an enzyme experiment, the reaction rate (measured in mol/min) is the dependent variable — it responds to temperature changes.”

“In a drug trial, the control group receives a placebo instead of the medication, allowing researchers to distinguish the drug's effect from the placebo effect.”

“In a plant growth experiment, soil type, pot size, and watering schedule are controlled variables — they are kept identical across all groups to isolate the effect of the tested variable.”

“A hypothesis might state: 'If the concentration of fertilizer is increased, then plant growth rate will increase proportionally.' ACT questions often ask whether experimental results support or contradict a given hypothesis.”

“If a table shows reaction rates at 10°C (50 units) and 20°C (200 units), interpolating the rate at 15°C would estimate approximately 125 units — within the known range.”

“If a graph shows bacterial growth increasing from 10°C to 37°C, extrapolating beyond the data suggests growth continues — but the actual trend (a decline at very high temperatures) shows extrapolation must be used cautiously.”

“In ACT Science graphs, a line sloping upward from left to right shows a direct (positive) relationship between the x and y variables.”

“A line sloping downward from left to right in an ACT graph shows an inverse (negative) relationship. Example: as altitude increases, air pressure decreases.”

“A single trial produces preliminary evidence; replication across multiple trials or by independent researchers establishes scientific credibility. ACT questions often ask what would 'strengthen' an experiment — adding replication is usually correct.”

“If researchers test whether coffee improves test scores but do not control for sleep hours, sleep deprivation is a confounding variable — it independently affects both coffee consumption and test performance.”

“ACT Science figures sometimes include error bars. If error bars for two groups overlap significantly, the difference between them may not be statistically meaningful.”

“A scatter plot with a trend line sloping upward indicates a positive correlation between the variables. ACT questions may ask you to predict a value by extending the trend line.”

“An ACT passage might show that ice cream sales and drowning rates both peak in summer — they are correlated, but ice cream does not cause drowning. Both are caused by hot weather (a confounding variable).”

“An ACT Science question might ask which of two effects has a greater magnitude — meaning which is larger in absolute value or relative change.”

“Many scholars read Orwell's Animal Farm as an allegory for Stalinist Russia, with the pigs representing the Soviet Communist Party leadership.”

“The author uses irony when a character who has lectured others about punctuality is the last to arrive at the meeting.”

“The author's juxtaposition of opulent vacation homes alongside abandoned factories illustrates the economic divide in the region.”

“The recurring motif of clocks and watches throughout the novel emphasizes the protagonist's obsession with time and mortality.”

“"The river moved like liquid silver through the valley" is a simile comparing the river to silver to suggest beauty and fluidity.”

“"Time is a thief" is a metaphor comparing time to a thief, suggesting that time takes things from us without warning.”

“"The wind whispered through the trees" personifies wind by giving it a human action (whispering).”

“"I've told you a million times" uses hyperbole — the speaker clearly has not literally told them a million times, but the exaggeration emphasizes frustration.”

“ACT Reading questions frequently ask why an author opens with an anecdote — usually to make an abstract concept concrete, to establish a personal connection with the reader, or to set up a contrast.”

“Referring to someone as a 'Trojan horse' alludes to the Greek myth, implying a seemingly helpful offer that actually conceals a threat.”

“Jonathan Swift's 'A Modest Proposal' is a famous example of satire — Swift ironically proposes eating Irish children as a solution to poverty to draw attention to British exploitation of Ireland.”

“"Less is more" is a paradox — acquiring fewer things often leads to greater clarity and satisfaction. ACT passages use paradoxes to signal complex, nuanced arguments.”

“ACT Reading questions frequently ask about an author's tone. Common tones: critical, celebratory, nostalgic, ironic, melancholy, reverent, sardonic, objective, sympathetic.”

“The mood of a passage is created by the author's word choices, pacing, and imagery. A passage describing an abandoned factory at dusk creates a melancholy, foreboding mood.”

“ACT Literary Narrative questions often distinguish between what the narrator believes vs. what other characters believe, or between the narrator's stated claims and implied attitudes.”

“The shifting demographic composition of the United States — with a growing elderly population — has significant implications for Social Security funding.”

“The ideological differences between the two parties reflect fundamentally different views on the proper role of government in managing the economy.”

“Socioeconomic status — measured by income, education, and occupation — is consistently among the strongest predictors of educational attainment and health outcomes.”

“Social stratification in industrialized economies is often reinforced by unequal access to educational resources, limiting upward mobility for lower-income groups.”

“Researchers studied how rates of cultural assimilation differed between first-generation immigrants, who retained many native cultural practices, and their American-born children.”

“Rapid urbanization in Southeast Asia has driven economic growth but has also strained infrastructure, increased pollution, and reduced agricultural land.”

“Investment in transportation infrastructure — roads, rail, ports — is widely regarded as one of the highest-return forms of public spending for long-term economic development.”

“The historian argued that economic hegemony, exercised through trade agreements and debt structures, was more powerful than military force in maintaining colonial relationships.”

“The Great Migration — the movement of approximately six million Black Americans from the rural South to northern cities between 1910 and 1970 — fundamentally transformed American urban culture.”

“Cultural pluralism holds that diverse ethnic communities should be able to maintain their distinct identities while participating fully in a shared civic life.”

“The sociologist was careful to distinguish empirical findings — supported by data from 10,000 survey respondents — from theoretical predictions about behavior.”

“The qualitative portion of the study involved in-depth interviews with 40 participants, capturing their lived experiences in ways that statistical data could not.”

“Quantitative analysis of the 50-year dataset revealed a statistically significant correlation between school funding and graduation rates across districts.”

“The longitudinal study tracked the cognitive development of 500 children from birth through age 18, providing data unavailable from shorter studies.”

“The discovery of a correlation between two variables does not establish causation; a randomized controlled trial is typically needed to demonstrate a causal relationship.”

“ACT Science passages about plant physiology often use photosynthesis as context. Knowing the basic inputs (CO₂, water, light) and outputs (glucose, oxygen) helps you interpret data about plant growth.”

“An ACT experiment might measure how plant cells respond to solutions of different concentrations — osmosis drives water into or out of the cells depending on relative concentration.”

“Enzymes act as biological catalysts, dramatically increasing reaction rates in living cells. An ACT experiment might study how temperature or pH affects enzyme (catalytic) activity.”

“The passage explained that without energy input, systems naturally move toward greater entropy — more disordered, less organized states.”

“In ACT chemistry-related passages, equilibrium refers to the point at which a reaction's forward and reverse rates balance, resulting in stable concentrations of reactants and products.”

“Rusting is a form of oxidation — iron reacts with oxygen and water to form iron oxide. ACT passages about corrosion or combustion may reference oxidation reactions.”

“An ACT Natural Science passage might describe the taxonomic classification of a newly discovered organism and ask you to infer its characteristics based on its classification.”

“The passage argued that tropical rainforests contain the greatest biodiversity of any terrestrial ecosystem, housing an estimated half of all known species despite covering only 6% of the Earth's surface.”

“The geologist identified the canyon walls as sedimentary rock, formed layer by layer over millions of years. ACT Earth Science passages may reference sedimentary layers (strata) as records of geological time.”

“The electromagnetic spectrum spans from radio waves (long wavelength, low energy) to gamma rays (short wavelength, high energy), with visible light occupying a narrow band in between.”

“ACT Earth Science passages on earthquakes and volcanic eruptions often reference tectonic plate boundaries — the edges where plates meet, diverge, or slide past each other.”

“In a double-blind clinical trial, neither participants nor researchers know who received the drug and who received the placebo, preventing bias from influencing the results.”

“Oxygen diffuses from the air sacs of the lungs into the bloodstream because its concentration is higher in the lungs than in the blood — a passive, energy-free process.”

“An ACT Biology passage might describe the stages of mitosis — prophase, metaphase, anaphase, telophase — and ask about the purpose or result of each stage.”

“A graph showing light absorption by different pigments would plot wavelength on the x-axis. Chlorophyll absorbs red and blue wavelengths most strongly and reflects green wavelengths — which is why leaves appear green.”

“The columnist's sardonic description of the policy summit — 'three days of speeches that produced a 40-page document no one will read' — conveyed deep skepticism about political process.”

“The narrator's ambivalent attitude toward her childhood home — drawn by memories yet repelled by painful associations — creates the passage's emotional tension.”

“The biographer adopted a reverent tone when describing the physicist's decades of dedication to pure research, treating her subject as almost saintly in her commitment to knowledge.”

“The author's pragmatic argument — that the policy should be evaluated by its measurable outcomes, not its stated intentions — contrasted sharply with the idealistic rhetoric of its proponents.”

“The essay's nostalgic tone — evident in the detailed, warm descriptions of childhood summers in the rural South — suggests the author views the past through a lens of idealization.”

“The journalist's cynical view of corporate philanthropy — 'generosity calibrated to maximize tax benefits' — implied that no act of apparent altruism is genuinely selfless.”

“The activist's fervent prose — peppered with exclamation points and urgent calls to action — left no doubt that the author viewed the cause as a moral imperative.”

“The essay closes on a melancholy note, as the author returns to find the neighborhood of her childhood completely transformed, its unique character replaced by generic commercial development.”

“The researcher's tentative conclusions — 'these results suggest, though do not prove' — reflected appropriate scientific caution given the study's small sample size.”

“ACT Reading questions that ask about an author's tone toward a subject — when the author points out flaws, contradictions, or harms — often have 'critical' as the correct answer.”

“The author failed to substantiate her central claim about economic inequality with specific data, relying instead on general assertions and anecdotes.”

“The follow-up study refuted the original hypothesis by producing results in the opposite direction — a decrease in performance, not the predicted increase.”

“The author concedes that economic development has reduced absolute poverty in many regions, but argues that relative inequality has simultaneously increased.”

“The author asserts that early childhood education is the most cost-effective public investment available — a claim supported by decades of longitudinal research.”

“Multiple independent studies corroborate the finding that physical exercise improves cognitive function in both children and adults.”

“The economists extrapolated from existing trends to predict that — without intervention — income inequality would continue to widen through 2050.”

“The leaked documents undermined the corporation's claims of transparency, revealing that internal reports had been withheld from regulators.”

“The field trial validated the laboratory findings by reproducing the same results in real-world conditions across three different geographic regions.”

“Darwin postulated natural selection as the mechanism of evolution decades before the molecular evidence for genetics provided direct confirmation.”

“ACT Science Conflicting Viewpoints questions sometimes ask what evidence would help reconcile the two scientists' different explanations — meaning what would make their views compatible.”

“The archivist's meticulous restoration of the damaged manuscripts — each page cleaned and catalogued individually — preserved documents that would otherwise have been lost.”

“The artist specialized in ephemeral installations — sculptures made from ice or sand — that existed for only hours before dissolving back into their component materials.”

“Smartphones have become so ubiquitous that their presence in every pocket, meeting, and restaurant has fundamentally altered how people relate to each other in public spaces.”

“The monastery's austere architecture — bare stone walls, small windows, no ornament — reflected the monks' conviction that beauty was a distraction from contemplation.”

“The prolific author wrote over 80 novels, 400 short stories, and countless essays during a career spanning six decades.”

“The executive summary was succinct — just three paragraphs distilling a 150-page report into the most essential findings and recommendations.”

“The professor's nuanced analysis of immigration policy rejected both the 'pure benefit' and 'pure harm' narratives, tracing specific costs and benefits across different communities.”

“The connection between the two events was tenuous — separated by a decade and connected only by a superficial resemblance in their outcomes.”

“The reviewer noted that the third chapter was tangential to the book's central argument and could be removed without weakening the core thesis.”

“The unprecedented scale of the climate event — affecting every continent simultaneously — challenged existing emergency response frameworks designed for regional disasters.”