No. In the acquisition of knowledge, principles and elements are not always known first, because sometimes from sensible effects we arrive at the knowledge of principles and intelligible causes.
In accipiendo scientiam, non semper principia et elementa sunt priora, quia quandoque ex effectibus sensibilibus devenimus in cognitionem principiorum et causarum intelligibilium.
But if our intellect understood by participation of certain separate indivisible (forms), as the Platonists maintained, it would follow that a like indivisible is understood primarily; for according to the Platonists what is first is first participated by things.
Si autem intellectus noster intelligeret per participationem indivisibilium separatorum, ut Platonici posuerunt, sequeretur quod indivisibile huiusmodi esset primo intellectum, quia secundum Platonicos, priora prius participantur a rebus.
The object of our intellect in its present state is the definable structure of a material thing, which it abstracts from the phantasms, as above stated (Q84, A7). And since that which is known first and of itself by our cognitive power is its proper object, we must consider its relationship to that definable structure in order to discover in what order the indivisible is known.
Obiectum intellectus nostri, secundum praesentem statum, est quidditas rei materialis, quam a phantasmatibus abstrahit, ut ex praemissis patet. Et quia id quod est primo et per se cognitum a virtute cognoscitiva, est proprium eius obiectum, considerari potest quo ordine indivisibile intelligatur a nobis, ex eius habitudine ad huiusmodi quidditatem.
Now the indivisible is threefold, as is said De Anima iii, 6.
Dicitur autem indivisibile tripliciter, ut dicitur in III de anima.
The third kind of indivisible is what is altogether indivisible, as a point and unity, which cannot be divided either actually or potentially. And this indivisible is known secondarily, through the privation of divisibility.
Tertio modo dicitur indivisibile quod est omnino indivisibile, ut punctus et unitas, quae nec actu nec potentia dividuntur. Et huiusmodi indivisibile per posterius cognoscitur, per privationem divisibilis.
This indivisible has a certain opposition to a corporeal being, the definable structure of which is the primary and proper object of the intellect.
Et huius ratio est, quia tale indivisibile habet quandam oppositionem ad rem corporalem, cuius quidditatem primo et per se intellectus accipit.