Short answer. A new trial is available on two grounds a plain motion for reconsideration cannot reach: fraud, accident, mistake, or excusable negligence that impaired your rights despite ordinary prudence, or newly discovered evidence that reasonable diligence could not have produced at trial and that would probably change the result.
What the law says
Fraud, accident, mistake or excusable negligence which ordinary prudence could not have guarded against and by reason of which such aggrieved party has probably been impaired in his rights; or (b) Newly discovered evidence, which he could not, with reasonable diligence, have discovered and produced at the trial, and which if presented would probably alter the result.
Rule 37, Section 1 — Grounds of and period for filing motion for new trial or reconsideration. Read the full provision →
Fraud, accident, mistake, or excusable negligence
The first ground for a new trial is fraud, accident, mistake, or excusable negligence that ordinary prudence could not have guarded against, and that has probably impaired the aggrieved party's rights. This ground looks backward at what went wrong before or during trial — a surprise beyond the party's control that kept them from fully presenting their case, not a disagreement with how the court weighed the evidence it did receive. Because the rule requires that ordinary prudence could not have prevented it, a mistake or oversight the party's own lack of diligence caused will not qualify.
Newly discovered evidence
The second ground is newly discovered evidence — evidence the party could not, with reasonable diligence, have discovered and produced at the trial, and which, if presented, would probably alter the result. Both elements matter: the evidence must have been genuinely undiscoverable through diligent effort at the time, not simply evidence the party failed to gather, and it must be strong enough that the outcome would probably change, not merely add detail to what the court already considered.
What reconsideration covers instead
A motion for reconsideration, filed within the same period, rests on different grounds entirely: that the damages awarded are excessive, that the evidence already on record is insufficient to justify the decision or final order, or that the decision or final order is contrary to law. None of these require anything new — they ask the trial court to revisit its own reasoning on the existing record, rather than to reopen the case for grounds the party could not have raised before.
Same deadline, different remedies
Both motions must be filed within the period for taking an appeal, so a party choosing between them is working against the same clock rather than a separate one for each. The choice comes down to what actually went wrong: if the problem is something the existing record already shows — an error of law, excessive damages, or evidence found wanting — reconsideration fits. If the problem is a fair trial undermined by fraud, accident, mistake, excusable negligence, or evidence that could not have been produced earlier, a new trial on one or both of those causes is what the rule provides.