Law test preparation
Ascend Ivy Team · · 4 min read
An assumption fills a gap between an argument’s evidence and its conclusion. Finding that gap is different from deciding whether you like the conclusion. A useful first exercise is to write what the author knows, what the author concludes, and what must connect the two.
Read the guide
LSAC describes logical reasoning as analyzing arguments, including their parts, assumptions and flaws. Begin by identifying the conclusion the author wants you to accept. Then identify the evidence offered for it. Background context can help explain the situation without itself supporting the conclusion.
Do this before deciding what an answer should say. An answer choice can be true in everyday life and still fail to address the question. Work within the information provided by the argument.
A town extended its library’s opening hours. Total visits rose the following month. Therefore, extending the hours caused the increase in visits. The evidence is the timing of the change and the increase; the conclusion is a causal claim.
The gap is that another factor could explain the increase. Perhaps a popular exhibition opened during the same month. That possibility does not prove longer hours had no effect. It shows why the evidence alone does not establish the claimed cause.
If asked what weakens this argument, a relevant alternative explanation may matter. If asked what strengthens it, evidence reducing a plausible alternative may help. If asked for a necessary assumption, ask what the reasoning depends on; do not merely choose something that would make the story more convincing.
Necessary and sufficient assumptions are different tasks. A necessary condition must hold for the reasoning to work, but may not guarantee the conclusion. A sufficient condition, if added, must be strong enough to establish the required inference. Check the exact wording before using any shortcut.
Suppose an argument says every application received before Friday will be reviewed, and concludes that Maya’s application will be reviewed. One way to complete the reasoning is to establish that Maya’s application was received before Friday. Without additional information, the first statement alone does not establish when hers arrived.
That statement is sufficient to support the conclusion in this miniature argument. It is not necessarily required for Maya to receive a review: the rule did not say late applications can never be reviewed. This is why treating every useful statement as a necessary assumption creates errors.
During review, identify whether the rejected choice concerned the wrong group, reversed a relationship, used a stronger claim than needed or merely repeated a premise. Make the explanation specific to the argument. “Out of scope” is a label, not a complete explanation.
On a fresh question, see whether you can identify the same reasoning distinction without remembering a prior answer. Begin untimed when learning a concept; move to current official practice for format and pacing work.
The examples on this page were written for teaching and are not licensed LSAC questions. They are intentionally short so you can see the logical distinction. They do not reproduce the range or difficulty of a complete test.
Our reasoning collection offers additional original exercises and explanations. LawHub supplies official LSAT preparation. Choose the resource for the job you need: understanding an inference, practicing a skill, or becoming familiar with the official test interface.
Use a free LSAT review log to test the distinction on fresh material
Put it to work
Before looking at choices, complete these lines for one argument.
From the Ascend Ivy library
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LSAT reasoning practice
Original LR and RC instructional practice with twenty study lessons, paragraph evidence and fillable responses. Four reading sets include a paired comparison. This is not a licensed or calibrated exam form.
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Official sources checked October 8, 2026. The provider or program’s current instructions take precedence. Original examples are teaching material, not applicant submissions. About our research, AI assistance and corrections.