Many Reformed reject it: God knows conditional truths, but from his free decree, not before it
Many other Reformed theologians, however, reject this middle and conditional knowledge in God as empty and superfluous. They do not all do so in the same way, though, or rely on the same grounds.
First, some grant that every proposition denying or affirming that something will happen contingently, under any condition, is determinately true or false, and so knowable by God. No one doubts that God knows and grasps every truth with certainty. So they affirm that no question about free and conditional future things that a human or angelic mind can imagine is one God cannot answer clearly: given this or that condition, the matter will turn out thus.
Yet they deny that it follows that God has any conditional knowledge preceding his free decree. God does know these things, but from the free decree of his will. By that decree he predefined with himself from eternity the modes and connections not only of things that will happen in time but also of things that never will and are merely possible. There is this difference: the former he willed to happen, the latter he did not. Yet if he had willed them, they would happen just as he had predefined.
These are the words of Matthias Nethenus, given in the work of the celebrated Gisbertus Voetius and approved by Voetius himself: Theological Disputations, part 1, theses on conditional or middle knowledge in God, section 3, number 18.
Latin
XXXII. Verum plures alii Reformatorum Theologi scientiam istam Mediam & conditionatam in Deo tanquam vanam & superfluam rejiciunt: non omnes tamen eodem modo, neque iisdem fundamentis nitentes. Et primo quidem nonnulli sunt qui concedunt omnes propositiones quae negant vel affirmant contingenter aliquid futurum, sub quacunque conditione, determinate veras vel falsas esse, ac proinde etiam a Deo cognoscibiles; nec enim ulli dubium est quin Deus omnem veritatem certo cognoscat atque apprehendat. Adeoque affirmant nullam esse quaestionem de futuris liberis & conditionatis, ab humano vel angelico intellectu imaginabilem, ad quam non perspicue respondere possit Deus, posita hac vel illa conditione, rem sic se habituram. Negant tamen inde sequi ullam esse in Deo scientiam conditionatam, quae liberum Dei decretum antecedat. Idque quoniam Deus ista quidem scit, sed ex libero voluntatis suae decreto, qua non tantum modos & connexiones rerum in tempore futurarum, sed etiam nunquam futurarum, & tantum fieri possibilium, apud se ab aeterno praefinivit; sed cum isto discrimine, quod ista fieri vellet, haec nollet: quae tamen si vellet, sic futura essent quemadmodum praefinierat. Quae sunt verba Matthaei Netheni apud Gisbertum Voetium, virum Celeberrimum, & eodem Voetio probante, Disputationum Theologicarum parte prima thesibus de conditionata sive Media in Deo scientia sectione tertia, num. 18.