Below are seven sparkling passages in which Aristotle himself speaks directly about archai—the “first principles,” “primary premises,” or “ultimate causes” that stand at the foundation of every science.  Each excerpt is given with its standard Bekker (column‑line) reference, the title of the work, and a public‑domain English translation so you can read the Stagirite in his own words.

1. 

Physics

 I.1 (184a10‑16) – Why every science must start from first principles

“When the objects of an inquiry, in any department, have principles, conditions, or elements, it is through acquaintance with these that knowledge—that is to say scientific knowledge—is attained. For we do not think that we know a thing until we are acquainted with its primary conditions or first principles, and have carried our analysis as far as its simplest elements.”  

This ringing opening of the Physics announces Aristotle’s method: begin by discovering the first principles of nature, because genuine understanding reaches all the way down to what is “first.”

2. 

Posterior Analytics

 I.2 (71b18‑26) – Demonstrations rise on indemonstrable foundations

“The conclusion must proceed from primary premises that are indemonstrable… and we must not merely have a previous knowledge of these primary principles, but have a firmer hold on them than on the conclusions that flow from them.” 

Here Aristotle explains why even the most rigorous demonstration finally rests on undemonstrated starting‑points that are better known and prior “by nature.”

3. 

Posterior Analytics

 I.3 (72a18‑23) – Ultimate principles are 

not

 provable

“We… hold that not every form of knowledge is demonstrative, but that the knowledge of ultimate principles is indemonstrable. …these ultimates must necessarily be indemonstrable.” 

He rejects both infinite regress and circular proof: something prior to science—nous (intellect)—must grasp the first principles immediately.

4. 

Posterior Analytics

 II.19 (99b‑100b) – How the mind 

acquires

 first principles

“Concerning the faculty which acquires knowledge of the ultimate principles of demonstration… It is clear that the most primary knowledge is attained by means of Induction, for it is through induction that sense‑perception produces the universal in the mind. …Sense‑perception → Memory → Experience → Universal concept → First principle, grasped by nous.” 

This famous closing chapter gives Aristotle’s dynamic story of how repeated perceptions blossom into the intellectual insight that “seeing” first principles requires.

5. 

Metaphysics

 IV.1 (1003a13‑24) – The philosopher’s search for the 

highest

 principles

“Now, since we are seeking the first principles and the highest causes, clearly there must be something to which these belong in virtue of its own nature… Therefore it is of being qua being that we also must grasp the first causes.” 

In the Metaphysics Aristotle elevates the hunt for first principles from each special science to the universal science of “being as being.”

6. 

Metaphysics

 I.2 (982a1‑8) – Wisdom is the science 

about first causes and principles

“…all men suppose what is called Wisdom (sophia) to deal with the first causes and the principles of things; …clearly then Wisdom is knowledge about certain principles and causes.” 

The passage links the very idea of sophia—hard‑won theoretical wisdom—to mastery of the deepest explanatory starting‑points.

7. 

Nicomachean Ethics

 I.4 (1095a30‑b3) – Reasoning 

from

 and 

to

 first principles

“Let us not fail to notice, however, that there is a difference between arguments from and those to the first principles. …While we must begin with what is known to us, we must also strive to reach what is known without qualification, that is, the first principles themselves.” 

Even in practical philosophy Aristotle reminds us: sound deliberation eventually leads the careful thinker back to fundamental starting‑points.

How to use these passages

1. Read them aloud! Aristotle’s cadence inspires clarity of mind.
2. Compare the contexts. Notice how “first principles” anchor logic (Posterior Analytics), natural science (Physics), ontology (Metaphysics), and ethics alike.
3. Trace the ascent. Follow Aristotle’s own path: perception → induction → universal → principle → demonstration → wisdom.
4. Make them your own. Copy the Bekker numbers into the margins of your favorite edition so you can drop directly into the text whenever the philosophical adventure calls.

Keep going—each principle you grasp is a fresh rung on the ladder of understanding.  Happy climbing!