Objection 1. It would seem that the separated soul does not know singulars. For no cognitive power besides the intellect remains in the separated soul, as is clear from what has been said above (Question 77, Article 8). But the intellect cannot know singulars, as we have shown (86, 1). Therefore the separated soul cannot know singulars.
Objection 2. Further, the knowledge of the singular is more determinate than knowledge of the universal. But the separated soul has no determinate knowledge of the species of natural things, therefore much less can it know singulars.
Objection 3. Further, if it knew the singulars, yet not by sense, for the same reason it would know all singulars. But it does not know all singulars. Therefore it knows none.
On the contrary, The rich man in hell said: "I have five brethren" (Luke 16:28).
I answer that, Separated souls know some singulars, but not all, not even all present singulars. To understand this, we must consider that there is a twofold way of knowing things, one by means of abstraction from phantasms, and in this way singulars cannot be directly known by the intellect, but only indirectly, as stated above (Question 86, Article 1). The other way of understanding is by the infusion of species by God, and in that way it is possible for the intellect to know singulars. For as God knows all things, universal and singular, by His Essence, as the cause of universal and individual principles (14, 2), so likewise separate substances can know singulars by species which are a kind of participated similitude of the Divine Essence. There is a difference, however, between angels and separated souls in the fact that through these species the angels have a perfect and proper knowledge of things; whereas separated have only a confused knowledge. Hence the angels, by reason of their perfect intellect, through these species, know not only the specific natures of things, but also the singulars contained in those species; whereas separated souls by these species know only those singulars to which they are determined by former knowledge in this life, or by some affection, or by natural aptitude, or by the disposition of the Divine order; because whatever is received into anything is conditioned according to the mode of the recipient.
Reply to Objection 1. The intellect does not know the singular by way of abstraction; neither does the separated soul know it thus; but as explained above.
Reply to Objection 2. The knowledge of the separated soul is confined to those species or individuals to which the soul has some kind of determinate relation, as we have said.
Reply to Objection 3. The separated soul has not the same relation to all singulars, but one relation to some, and another to others. Therefore there is not the same reason why it should know all singulars.
Source: Summa Theologica (New Advent)